Topic 1: Growth

Concept of growth

Growth is the permanent and irreversible increase in size and dry mass of an organism.

But for growth to occurs the rate of cell increase must exceed the rate of cell loss.

When the rate of cell increase is higher than the rate of cell loss, growth is referred to as positive growth.

When the rate of cell increase is lower than the rate of cell loss, growth is referred to as negative growth.

Negative growth, the organism decrease in size and weight.

It may be caused by an illness or starvation.

Question

Why growth is said to be irreversible?

Answer. Because an organism cannot resume the size, weight and body shape of a newly born body.

DEVELOPMENT

Is the change in the complexity of an organism.

It involves differentiation and formation of various tissues that perform specialized functions.

NB: Growth is quantitative i.e. can be measured e.g. height, volume, mass) While Development is qualitative i.e. cannot be measured e.g. Emergence of a new structure, ripening of fruits.

IMPORTANCE OF GROWTH IN LIVING THINGS

1. Growth brings about an increase in the dry mass of an organism.

2. Growth gives rise to a more complex and elaborate multicellular organism.

3. Growth brings about the increase in size of an organism.

4. Growth enables organisms to adapt different environments.

5. Growth brings about cell specialization and enables cells to perform their specific functions.

Examples;

> Red blood cells carry oxygen> White blood cells fight pathogens

> Palisade cells carry out Photosynthesis

> Guard cells close and open stomata

Growth and development in multicellular organisms is brought about by the following processes.

i. Cell assimilation

ii. Cell division

iii. Cell enlargement or expansion

iv. Cell differentiation.

CELL ASSIMILATION

Is the incorporation of the materials absorbed from the surrounding into the cell metabolism.

The materials (food and respiratory gases) are used to make new structures of the cell

CELL DIVISION

This is the process whereby a single mother cell rises to several daughter cells.

Cell division is the basic of growth in all multicellular organisms as it results to increase in number of cells in the body.

CELL ENLARGEMENT

This refers to the increase in size of the cells as they absorb water by osmosis.

CELL DIFFERENTIATION

This is a process whereby the cells become specialized to their specific functions.

For example: red blood cells specialized for transporting respiratory gases, white blood cells specialized for fighting against diseases.

TYPES OF GROWTH

There are several types of growth namely: –

1. Allometric growth

2. Diffuse growth

3. Localized growth

4. Intermittent growth

5. Isometric growth

6. Determinate growth

7. Indeterminate growth.

1. ISOMETRIC GROWTH

Is the type of growth whereby all body organs grow at the same rate.

Or is growth that occurs when an organ grows at the same rate as the rest of the body.

Example of isometric growth

> Growth in fish and locust

2. ALLOMETRIC GROWTH

Is the type of growth whereby different parts of the body of an organism grow at different rates and stop growing at different times.

Or is growth that occurs when an organ grows at a different rate from the rest of the body

Example of allometric growth

> In humans the brain grows faster initially than other organs and virtually stops soon after the age of five years.

> In plants flowers grow faster than the vegetative parts.

> In almost animals the last organs to develop and differentiate are the reproductive organs

3. DIFFUSE GROWTH

Is the type of growth whereby growth occurs all over the body of an organism.

Example of diffuse growth

Growth in mammals.

4. LOCALIZED GROWTH

Is the type of growth whereby growth occurs in certain regions.

Example of localized growth

Growth in plants where growth takes place at the tips of roots and shoots. These tips are called meristems.

5. LIMITED GROWTH

Is the type of growth shown by organisms that stop growing when a certain body size or age is attained.

Or is growth that ceases at maturity.

Limited growth is also called Determinate growth or definite growth

Example of limited growth

Growth in mammals, birds and annual plants.

6. UNLIMITED GROWTH

Is the type of growth shown by organisms that do not stop to grow.

Unlimited growth is also called Indeterminate growth or indefinite growth

Example of unlimited growth

Growth in perennial plants, shrubs, corals, fish, reptiles etc.

7. INTERMITTENT GROWTH

Is a type of growth in arthropods in which growth takes place in a series of stages called instars.

Example of intermittent growth

Growth in insects where an egg hatches into a larva which then develops into a pupa and finally into an adult (imago).

METHODS USED TO MEASURE GROWTH

Growth can be measured by investigating the changes in the following parameters: –

i. Length

ii. Weight

iii. Height

iv. Volume

v. Number (population) at a suitable intervals of time.

i. LENGTH

This method is reliable if growth occurs mainly in one direction.

Increase in length denotes growth.

In plants for example leaves, stem and internodes on stems can be measured.

Advantages

i. The change in length is easy to work out.

ii. The same organism is used throughout the investigation.

iii. The organisms are not harmed.

Disadvantages

It ignores growth in other directions such as width and girth, which can be significant.

ii. VOLUME

This involves placing an organism in water filled container and determine the water displacement using an overflow can.

The volume of the water displaced by organism is measured by using measuring cylinders.

Advantages

It is easy to use

Disadvantages

The organisms are often irregular and changes in fresh weight which can misleading.

iii. TOTAL FRESH WEIGHT (MASS)

This method involves weighing the whole organism at regular intervals.

This is an easy method used to estimate growth in large animals including man.

Advantages

a. Weighing is easy

b. It does not involve injury to the organism.

Disadvantages

Does not always give accurate results due to the method is influenced by changes in water content of the body.

iv. DRY MASS (WEIGHT)

It involves killing the organism and heating it at 1100c to a constant weight to remove water.

Is used to measure growth of small organisms such as germinating wheat.

Advantages

a. It is more accurate

b. It indicates the increase in weight due to synthesis of different materials irrespective of water content.

Disadvantages

a. It is difficult to use.

b. The method involves killing the organisms and thus has limited usage.

c. A large number of organisms are used, hence the method is wasteful.

v. WIDTH

The width of parts of an organism can be measured over a period of time.

Advantages

a. Width is easily measured

b. The same organism is used to monitor growth.

Disadvantages

a. Increase in width interpreted as the only aspect of growth occurring.

(vi) NUMBER

Is the method used to measure growth in unicellular organisms such as bacteria, algae and protozoa

It involves collecting and counting the number of organisms in samples of fixed volume periodically.

These organisms are grown in cultures.

The total population can be estimated as follows:

Where

A =Average number of organisms per sample

B = Total volume of the sample.

C = Volume of the sample

N =Total population number.

THE GROWTH CURVES

Is a graph obtained when the growth parameters such as height, mass, volume and number are plotted against time.

A growth curve shows the growth pattern of an organism

For many population, organisms show the S-shaped growth curve called sigmoid curve

SIGMOID CURVE

Is the S-shaped growth curve

PARTS/ PHASES OF SIGMOID CURVE

The Sigmoid curve has four phases, namely:

i. Lag phase

ii. Log phase (exponential phase)

iii. Linear phase (decelerating phase)

iv. Stationary phase (plateau phase)

DIAGRAM OF SIGMOID CURVE

The pattern of growth tends to be the same in most organisms where slow at first, and then it speeds up and finally slows down as adult size is reached.

(a) LAG PHASE

Is the initial stage where little growth occurs.

It is the period when the rate of growth is very slow.

In some organisms there might be slight decrease in growth. E.g. in flowering plants there is loss in dry weight during seed germination.

Reasons for slow growth in this phase

i. The number of dividing cells is small.

ii. The cells have not yet adjusted to new environment.

iii. High catabolic rate than anabolic rate.

iv. Organisms are adapting to the new environment and are preparing for growth.

v. The number of individuals engaging in reproduction or the number of cells engaging in division is small.

(b) LOG OR RAPID (EXPONENTIAL PHASE)

Is the stage where maximum growth occurs.

In plants is the period where foliage increase in amount.

Reasons for rapid growth in this phase

i. Large number of dividing cells

ii. The rate of cell increase is greater than the rate of cell death.

iii. The cells have adjusted to the environment.

iv. Environmental factors such as food, space, air, and nutrients are in plentiful supply.

(c) DECELERATING PHASE

Is the stage at which maximum peak is reached and growth start to decline.

This is due to limiting factors that set in both internal & external.

Reasons for growth decline in this phase

i. Most cells have fully differentiated hence cannot undergo more differentiation.

ii. The rate of cell death is more than the rate of cell increase.

iii. Accumulation of waste products which could be harmful to organisms.

iv. Limitation by environmental factors e.g. shortage of food, air space.

(d) STATIONARY PHASE (PLATEAU)

Is the period when there is no further change in size of the organisms.

The organism has attained maturity

NB; Growth does not stop, but the rate of cell formation is equal to the need for cell replacement.

Reasons for stationary growth

The rate of cell increase equals the rate of cell death.

In microorganisms the number of individuals dying almost equals the number of new individuals formed.

FACTORS AFFECTING GROWTH IN PLANTS AND ANIMALS

Growth in plants and animals is influenced by a number of factors, which can be grouped into two categories namely:

A. Internal factors

B. External factors.

(B) EXTERNAL FACTORS AFFECTING GROWTH IN ANIMALS

The following are external factors affecting growth in animals

i. Temperature

ii. Diseases

iii. Nutrition

iv. Oxygen

(i) TEMPERATURE

Since optimum temperature increase the rate of metabolism and very low temperature slow down metabolism, therefore animals grow is faster in optimum temperature (warm climate). For example, a tadpole will grow faster in a warm pond than in a cold pond.

(ii) DISEASES

Both communicable and non-communicable diseases affect the rate of growth of an animal especially during childhood. For example, disease like diarrhea tends to inhibit absorption of nutrients that are essential for growth.

(iii)NUTRITION

Nutrition is very important for animal growth. Nutrients, especially proteins are very vital for growth. Inadequate amount of protein leads to stunted growth.

(iv) OXYGEN

The amount of oxygen has no much effect on the growth of terrestrial animals as it is readily available in the atmosphere.

However, it can have an impact on the growth of aquatic animals if its amount in water varies.

(b) INTERNAL FACTORS AFFECTING GROWTH IN ANIMALS

The following are internal factors affecting growth in animals

i. Genetic makeup (heredity)

ii. Hormones

(i) GENETIC MAKE UP

Animal growth is affected by genetic make up of an organism. Certain genetic constitution favours greater growth rates and greater body size while others do not. Also genetic disorders may restrict growth. Such disorders include achondroplasia in humans.

NB: Achondroplasia is a disorder that is characterized by shortened body, legs and hands.

(ii) HORMONES

Hormones have a great influence in growth of the animal. For example, over secretion of growth hormones during childhood results into Gigantism (giantism) while under secretion of growth hormones results into Dwarfism. Under secretion of thyroxine during development slows physical and mental development in human beings hence Cretinism.

NB: Cretinism is a condition in which a child become stunted and mentally retarded due to under-secretion of thyroxine hormone.

FACTORS AFFECTING GROWTH IN PLANTS

(a) INTERNAL FACTORS

The following are internal factors affecting growth in plants

i. Heredity factors

ii. Growth hormones

iii. Apical dominance

(i) HEREDITY FACTORS

Various characteristics of a plant such as growth pattern, flower colour, number of floral parts are controlled by heredity factors or genes which are found in the chromosomes inside the nucleus of the cells. These genes affect physical appearance and the size of a plant.

(ii) GROWTH HORMONES

Hormones are chemical substances that influence physiological processes. Growth hormones affect growth which is brought about by cell division and enlargement.

In plants growth hormones are called Auxins and they are found at the apical meristems, where they promote growth at the tips of the roots and shoots.

(iii)APICAL DOMINANCE

Is the inhibition of the growth of lateral buds by the presence of growing apical buds.

The apical buds produce auxins that diffuse down the stem inhibiting growth and development of lateral buds

Apical buds are found at the top of the plant and they are responsible for increase in plants height (apical growth).

Lateral buds are found on the sides of the plant which are responsible for formation of branches.

A plant that has strong apical dominance gains more height in comparison to its width, and cause plant shoots to have a conical shape.

Lateral buds nearer to the tip are more affected by the apical dominance than lateral buds far away from the shoot tip because there is higher concentration of auxins at the shoot tip than other parts away from the shoot tip.

(b) EXTERNAL FACTORS (ENVIRONMENTAL FACTORS)

The following are external or environmental factors affecting growth in plants:

i. Plant nutrition

ii. Water

iii. Light

iv. Temperature

v. Relative humidity

vi. Carbon dioxide

vii. Soil

(i) PLANT NUTRITION

Plants absorb nutrients from the soil or surrounding environment. Nutrients are used for growth.

Lack of adequate nutrients leads to reduced growth.

For example, proteins are needed for plant growth. Absence of nitrate cause plant to look shorter than their real age (stunning).

(ii) WATER

Water is one of the most essential factors required in growth of plants. It plays a crucial role for efficient photosynthesis, respiration, transportation of minerals and other nutrient through the plant.

Water is also responsible for proper functioning of the stomata opening leaves.

(iii) LIGHT

The better growth of plant depends on the presence of light because light is one of the conditions needed for photosynthesis to take place. Therefore, little or absence of light causes plant to manufacture little or no food hence plants rate of growth become very poor.

(iv) TEMPERATURE

Temperature is very essential in the process of plant growth. Optimum temperature activates the enzymatic activities such as photosynthesis, metabolism and seed germination hence high growth rate. Very low temperature slows down metabolism hence low growth rate. Extremely high temperature kills cells and enzymes thus metabolism cannot take place hence death of a plant.

(v) AMOUNT OF CARBONDIOXIDE AND OXYGEN

The manufacturing of sugar by plants requires the presence of carbondioxide. It is thus one of the vital elements for plant growth. Oxygen is essential for plant respiration and utilization of the byproduct of photosynthesis.

(vi) SOIL

Soil with proper humidity and the right balance of all the minerals and nutrients is one of the essential factors in plant growth. Presence of required soil quality and required mineral influence growth and vice versa.

(vii) RELATIVE HUMIDITY

Is the ratio of water vapour in the air to the amount of water in the air.

Relative humidity affects the rate of transpiration in plant. Low humidity increases the rate of transpiration hence slowing growth as a plant will suffer from water stress.

DIFFERENCES BETWEEN GROWTH AND DEVELOPMENT

GROWTH	DEVELOPMENT
(i) It is quantitative	It is qualitative
(ii) It ends at maturation	It continues until an organism demise
(iii) It is dependent on cellular changes	It dependent on organizational transformation
(iv) It is external (physical appearance)	It is internal in nature (character of an individual)
(v) It focuses on size aspect	It focuses on emotional state, intelligence and interpersonal skills.

REVISION QUESTIONS

1. (a) Define the following terms as used in growth.

i. Growth

ii. Development

iii. Apical dominance

(b) Briefly explain the following statements.

i. Growth is quantitative.

ii. Fresh mass parameter is not reliable method of estimating growth of an organism.

(c) Briefly explain the following as used in growth.

i. Localized growth

ii. Intermittent grows

iii. Positive growth

iv. Cell division

2. List down four (4) importance of Growth.

3. Explain three (3) external and three (3) internal factors affecting growth in plants.

4. Explain three (3) external and three (3) internal factors affecting growth in animals.

5. Removal of the apical bud from the shrub is a practice that results in the development of the lateral buds which later form the branches.

(a) Give reasons for the development of the lateral branches after the removal of the Apical bud

(b)Suggest one application of this practice?

(c) What is the importance of this practice?

5. Explain why several auxillary buds sprout when a terminal bud in a young tree is removed.

MITOSIS AND GROWTH

Growth of an organism is brought by an increase in number of cells in the body of an organism.

The increase in number of cells in the body of an organism is brought about by cell division.

CELL DIVISION

Is the process by which a parent cell divides into two or more daughter cells.

TYPES OF CELL DIVISION

There are two types of cell division, namely:

i. Meiosis

ii. Mitosis

i. MITOSIS

Is the process in which cells divide during growth of an organism to form new cells which are similar to the parent cells.

During mitosis two daughter cells are formed

Each daughter cell has the same number of chromosomes as the parent cell.

Mitosis is the one which brings about growth of an organism by increasing the number of cells

Mitosis occurs in the somatic cells during the growth of an organism

QUESTION

1. Why mitosis is referred to as equatorial cell division? Briefly explain

ANSWER: Because it gives two daughter cells each with equal number of chromosomes as the original parent cell.

Cells in the body are classified into two categories according to the number of chromosomes found in the nucleus. These are:

i. Reproductive cells

ii. Somatic cells (body cells)

(i) REPRODUCTIVE CELLS

Are those cells which give rise to the formation of gametes.

They are found in the testes for males and in the ovaries for females

Reproductive cells contain unpaired chromosomes

(ii) SOMATIC CELLS

Are body cells that concern with growth of an organism.

They contain chromosomes that occurs in pairs.

The number of chromosomes in a body cell is referred to as diploid number (2n).

A human being has 46 chromosomes, a cat has 38 chromosomes, maize has 20 chromosomes and tomato has 24 chromosomes

STAGES OF MITOSIS

Mitosis consists of five (5) stages.

1. Interphase

2. Prophase

3. Metaphase

4. Anaphase

5. Telophase

1. INTERPHASE

Is the stage between one cell division and the next

It is a preparatory stage where a cell engages in many cellular activities before division.

The following events are observed during this phase (stage).

(i) Chromosomes appear as long and thin threads called chromatin threads within the nucleus

(ii) Chemical activities occur to build up reserve energy for cell division.

(iii) Cell organelle such as Centrioles, mitochondria and nucleotides replicate.

Consider the diagram below of interphase stage

 

2. PROPHASE

During this stage, the following events occur in the cell.

i. The chromosomes become short, thick and visible under light microscope.

ii. Each chromosome forms two sister chromatids attached at centromere.

iii. The nucleolus disappears.

iv. The nuclear membrane breaks down.

v. The Centrioles separate and migrate toward the opposite poles.

vi. Spindle fibres (spindle apparatus) appear but not fully developed.

NB. Spindle fibres

Are fine thread-like structures which radiate from Centrioles and control the movement of chromosomes.

Consider the diagram of prophase

3. METAPHASE

During this phase the following events take place

(i) The spindle fibres become fully developed.

(ii) The chromosomes arrange themselves at the centre (equator) with spindle fibres attached the centromeres.

N.B. Equator is the middle part of the cell.

Consider the diagram below

 

 

4. ANAPHASE

This phase is associated with the following events.

i. The centromeres separate.

ii. The spindle fibers shorten, pulling apart the sister chromatids towards opposite poles of the cell.

iii. At the end of this stage, chromatids reach at the poles.

Consider the diagram below

5. TELOPHASE

This is the last stage of mitosis. It is associated with the following events.

i. The spindle fibres disappear

ii. The chromatids become chromosomes which are less visible under light microscope.

iii. The nucleolus reappears.

iv. The new nuclear membrane reforms around each set of chromosomes.

v. In animal cell, Cytokinesis occurs.

N.B. Cytokinesis

is the process in which the cytoplasm of a cell constrict at the centre to divide a cell into two daughter cells.

vi. In plant cell, a cell plate is formed from vesicles and separates the cytoplasm of two daughter cells along the equator.

Consider the diagram below

 

SIGNIFICANCE OF MITOSIS

1. It results into genetic stability.

This is because the daughter cells produced tend to have similar number and type of chromosomes as the parent cell.

2. It is used as a means of reproduction for organisms reproducing asexually.

3. It repairs the body parts that have been damaged.

For example, when a finger is accidently cut with a knife, mitosis will give new cells to replace the damaged hence healing.

4. It is used in the regeneration of body parts which have been cut off.

For example, a cut off lizard tail can regenerate and return to its original state as a result of mitosis.

5. It is useful in the replacement of old cells in multicellular organisms.

DIFFERENCES BETWEEN MEIOSIS AND MITOSIS

MEIOSIS	MITOSIS
(i) It occurs in the reproductive cells to produce gametes.	It occurs in somatic (body) cells during growth and tissue repair.
(ii) Produced cells (gametes) fuse to form zygote.	New cells do not fuse to form a zygote.
(iii)Homologous chromosomes associate with one another.	Homologous chromosomes do not associate with one another.
(iv) Variation occurs through chromosome recombination.	No variation, all are like parents.
(v) Four daughter cells are formed from each parent cell.	Two daughter cells are formed from each parent cell.
(vi) It takes place in two phases to complete cell division	It takes place in one phase to complete cell division.
(vii)     Newly formed daughter cells are in haploid state	Newly formed daughter cells are in diploid state.

REVISION QUESTIONS.

1. Explain why;

(i) Mitosis is said to be equatorial cell division.

(ii) Mitosis is said to bring about growth.

2. The figure below shows the nucleus of a diploid cell during early stages of cell division.

i. How many pairs of chromosomes does it have?

ii. How many chromosomes does the nucleus contains?

iii. If a cell divides by mitosis, how many daughter cells will be produced?

iv. If a cell divides by meiosis, how many daughter cells will be produced?

v. How many chromosomes will each daughter cell have, at the end of;

a. Mitosis

b. Meiosis

GROWTH AND DEVELOPMENT IN HUMAN BEING

Human beings like other animals show growth and development.

Human beings show diffuse growth

DIFFUSE GROWTH

Is the pattern of growth whereby growth occurs all over the body of an organism.

Development includes growth, differentiation, wound healing, tissue regeneration, ageing and death.

The growth is usually rapid immediately after birth.

Human body organs grow at different rates hence show allometric growth

ALLOMETRIC GROWTH

Is the pattern of growth where body organs grow at different rates and stop growing at different times.

For example:

Reproductive organs grow slowly before puberty but they show very rapid growth during puberty.

Lymph tissue grows fast in early human life to produce Leucocytes for immunity.

NB: Like other mammals, human beings also show limited growth

LIMITED GROWTH

Is the growth that ceases at maturity.

In this case, the growth curve flattens or even decline prior to death.

The reason for decline is senescence.

SENESCENCE

Is a stage in the growth of human beings marked by the decline in smooth functioning of then organism, culminating to death.

GROWTH SPURT

Is a period of rapid growth in human being.

There are two growth spurts in human beings, one in early infancy and the other during adolescence.

In human beings, the growth curve in males is slightly different from females.

The difference occurs at adolescence where males keep on growing and developing faster than females.

Growth and development in female ends after puberty (around 16years). Males continue growing until they are 18 or 19 years.

FIGURE BELOW SHOWS THE HUMAN GROWTH CURVE

Growth and development in humans can be categorized into two groups, namely:

1. Pre-natal growth and development

2. Post-natal growth and development

1. PRE-NATAL GROWTH AND DEVELOPMENT

Is the growth and development takes place in the womb before a baby is born.

Pre – means before and natal – means birth

2. POST-NATAL GROWTH AND DEVELOPMENT

Is the growth and development that occurs after a baby is born.

It is the growth and development begins from birth to death.

Post – means after and natal – means birth.

STAGES OF HUMAN POST-NATAL GROWTH AND DEVELOPMENT

The human being post-natal growth and development has been divided into five main stages, namely:

i. Childhood or infancy stage

ii. Adolescences

iii. Adulthood

iv. Old age (senescence)

v. Death

NB: In each of the above stages, various physiological, psychological and behavioural changes take place

1. CHILDHOOD STAGE

Is the period from the time the baby is born up to sexual maturity.

Childhood stage is also called infancy stage

Childhood stage ranges from 0 – 11 years old

This stage requires adequate nutrition and care to promote physical and intellectual development.

Breast feeding is very important for the first two years to boost immunity.

Stages of childhood stage

Childhood stage is further divided into several stages, namely:

i. Neonatal

ii. Older baby

iii. Toddler

iv. Early childhood

v. Late childhood, and

vi. Pre-adolescence

i. NEONATAL STAGE

Is the stage from birth up to 5 months.

New babies are also called neonates.

PHYSICAL, PHYSIOLOGICAL, BEHAVIORAL AND PSYCHOLOGICAL CHANGES

THAT OCCUR DURING NEONATAL STAGE

Babies at this stage are helpless but can do a number of things such as crying, moving their arms, legs, heads, swallowing and sucking.

Babies at this stage suck anything put in their mouths.

They can grasp objects put in their hands

They spend most of their time sleeping

They can see but only a short distance of about 20cm.

They can hear, smell and feel.

The rate of heart beat is very high.

The baby shape change significantly from birth to 4 months. Initially, the head and abdomen are bigger compared to other body parts. The body becomes proportional as the baby grows up.

The baby can sit with support and respond to sounds. E.g. smiling upon hearing her mother’s voice.

Babies at this stage express their feelings mainly through crying. They cry to show hunger, thirst, pain, tiredness, fear and discomfort such as wet nappies, cold, a lot of heat and sickness.

The immune system is immature and the baby depends on the immunity from his or her mother through breast-feeding.

ADVANTAGES OF BREAST FEEDING

Breast feeding is very important than bottled milk due to the following reasons:

i. It creates a special bond between the mother and the baby.

ii. Breast milk is at the right temperature for the baby.

iii. Breast milk is well balanced and contains nearly all nutrients needed for normal functioning.

iv. Breast milk does not require preparation.

v. Breast milk is safe and free from contamination.

vi. Colostrum contains a lot of antibodies needed to protect the baby against infection.

vii. Breast milk is easily digested NB:

COLOSTRUM

Is the milk produced in the first days after delivery

Colostrum is usually sticky and yellow

It contains more proteins and antibodies than white milk produced later.

REASONS FOR SUBSTITUTION OF MOTHER’S MILK WITH COW’S MILK

i. Death of the Mother.

ii. Inability of the mother to produce enough milk.

iii. In case of multiple births e.g. twins and triplets.

iv. In case the mother has easily transmitted diseases like tuberculosis.

ii. OLDER BABY STAGE

This is the stage from 6 to 12 months.

PHYSICAL, PHYSIOLOGICAL, BEHAVIORAL AND PSYCHOLOGICAL CHANGES

THAT OCCUR DURING OLDER BABY STAGE

At 6 months, a baby can completely control his/her head and sit without support.

At 7 months the baby learns to crawl.

He/she can hold and drop objects and stand while holding things like tables or chairs.

The baby can use his or her hands to throw and point at things he/she wants using his/her index finger

Teething occurs at this period.

From 9 to 12 months the baby starts to walk.

The baby responds to his/her own name and other words that are familiar to him.

Social development also occurs at this period.

At 9 months, a baby can distinguish strangers from familiar people.

At 1 year, he/she understands and obeys simple commands like “come”.

iii. TODDLER STAGE

This is the age between 1 to 3 years.

PHYSICAL, PHYSIOLOGICAL, BEHAVIOURAL AND PSYCHOLOGICAL

CHANGES THAT OCCUR DURING TODDLER STAGE

Brain develops by 90%

The rate of heart beat is reduced to about 90-110 times per minute.

Immune system becomes mature.

Hearing has developed well.

The child is able to control micturition and defaecation as urinary and anal sphincter control become possible.

The baby can see everything that an adult can see.

All the 20 milk teeth appear by the age of 2.5 to 3 years.

At 12 to 14 months, the child uses gestures to express his/her feelings. For example, raising arms when he/she wants to be picked up.

At 15 months, the child copies what adults do. For example, a child may imitate “cooking” by taking a spoon and “stirring” it in a bowl.

At 15 to 18 months a child feeds him or herself.

A t 19 to 24 months a child likes to play with others (socialization), likes to dress and undress himself or herself.

He mimics social behaviours such as holding and feeding a toy.

At 25 to 36 months, a child can play with other children and share playing toys, can speak in a sentence, is more independent, can differentiate boys from girls, show preferences such as clothes and type of toys or games and knowhow to play different games.

Emotionally, children may feel jealousy, for example toward a new born baby.

They show fear for particular things like fear of some insects, dark and scary noise.

iv. EARLY CHILDHOOD

This is the age from 4 to 6 years.

At this stage, children go to kindergarten.

PHYSICAL AND PHYSIOLOGICAL CHANGES

A child has good appetite and therefore grows rapidly, Good appetite is important as children at their stage are very active and play a lot.

The child can identify up to five colours.

Motor coordination has developed well. Therefore, the child can walk, jump and skip.

Fine motor skills have also developed and the child can draw simple figures.

The child becomes curious and imaginative.

He/she understands right and wrong.

He/she becomes curious about sexuality.

The child can speak fluently, can tell his/her name, age and a simple story.

v. LATE CHILDHOOD

This is the age from 7 to 9 years.

At this stage, children are in primary school.

PHYSICAL AND PHYSIOLOGICAL CHANGES

Growth remains steady.

Children become very active.

The child can assume simple responsibilities like looking after the house when parents are not at home.

The child is very social and likes to socialize and belongs to groups.

He/she can help with household chores like washing dishes, setting the table, fetching water.

The child likes to associate with peers of similar interest.

This is the time children have friends and best friends. However, they prefer friends of the same sex.

Children at this stage can listen to peers opinion but still value opinions of their parents.

COMMON PROBLEMS IN CHILDHOOD STAGE (INFANCY STAGE)

i. Constipation

ii. Excessive crying

iii. Heat rash

iv. Nappy rash

v. Diarrhea

vi. Colic

(i) CONSTIPATION

This is the difficulty in passing out faeces.

This can be solved by giving fruit juice, vegetables and by increasing the baby’s intake of water.

(ii) EXCESSIVE CRYING

Crying is perfectly normal for babies but excessive crying indicates illness, pin, hunger, thirst, need for love and attention or the baby may be uncomfortable due to excessive heat or wetness.

(iii) HEAT RASH

Heat rash results to a rough itching skin, which may be painful caused by excessive heat.

Putting the baby in a cooler place and loosening the tight clothes may relieve this.

(iv) NAPPY RASH

The nappies should be changed frequently to avoid the nappy rash. The baby’s skin should be kept clean, dry and well oiled. Use of powder on the skin is recommended

(v) DIARRHOEA

Diarrhea may be a symptom of a disease or may be caused by overfeeding, infection or reaction to particular kind of food.

The baby should be given plenty of liquid to avoid dehydration.

In case of excessive diarrhoea, the baby should be taken to the nearest health center for treatment.

(vi) COLIC

A baby is said to have colic if it seems to be uncomfortable from pain in its abdomen.

This causes the baby to cry out loudly.

The pain is caused by airs swallowed at feeding time.

The baby should be held up with its abdomen leaning on the mothers shoulder to force the air out gently a condition known as winding up.

SERVICES REQUIRED TO MEET THE NEEDS OF CHILDREN

The services required to meet the needs of a child are in two categorizes, namely:

a. Essential (basic) services

b. Supportive services

(a) Essential (basic) services are necessary for baby’s survival.

> Healthy

> Warms.

> Shelter

> Clothing.

> Protection against illness and injury.

> Excessive and rest.

(b) Supportive services

Are services that will help a child to grow well socially, emotionally and mentally. Example of supportive services

> Love

> Care and comfort

> Security

> Training of habits and skills

> Older children need to be disciplined

> Trained to independent and useful to others and be responsible.

vi. PRE – ADOLESCENCE

This is the age from 10 and 11 years

PHYSICAL AND PHYSIOLOGICAL CHANGES

i. Growth starts to increase

ii. Appetite increase

iii. Secondary sexual characteristics start to show. For example, growth of breast and growth of public hair and hair under armpits.

iv. Children still prefer friends of the same sex.

v. Children are very social and tends to value peers opinion.

vii. ADOLESCENCE

Is a period in human developed between childhood and adult hood.

It generally occurs between the ages of 12 and 18 years.

At adolescence boys and girls attain sexual maturity (puberty),

viii. PUBERTY

Is the period when secondary sexual characteristics develop.

Girls attain puberty at the ages of 11- 13, boys attain puberty at the age of 12-14.

During adolescence, an individual experiences a lot of changes which includes emotional, social and physical changes.

These changes occur in both boys and girls to prepare their bodies for parenthood.

CHANGES IN BOYS ONLY AT PUBERTY

1. Shoulders and chest become broader (wider).

2. Muscles get stronger.

3. Beard grow.

4. The voice breaks (becomes deep)

5. Enlargement of sex organs and they occasionally emit some fluid from the penis at night (wet dream).

6. Sperm production starts.

CHANGES IN GIRLS ONLY AT PUBERTY

1. Enlargement of breasts.

2.  Widening of pelvic girdle (leads to enlargement of hips).

3. Ovulation starts.

4. Menstruation begins.

5. Enlargement of uterus and vulva.

CHANGES IN BOTH BOYS AND GIRLS AT PUBERTY

1.  Hairs grow in public region and under the armpits.

2. Sex hormones are secreted.

3. The skin sweats more often.

4. Attraction by members of the opposite sex.

5. Pimples may appear on the face but later disappear.

6. Body increases in size due to rapid growth.

SERVICES REQUIRED TO MEET THE NEEDS OF ADOLESCENCE

1. Healthy food for their growing bodies.

2. Peaceful home

3. Security and emotional support.

4. Cancelling

5. Physical exercise

6. Social skills

ix. ADULTHOOD STAGE

Adulthood starts at 20-55 years.

(i) Adults are physiologically, Psychological and Physical mature to make families.

Adulthood is divided into two categories, namely:

a. Early adulthood

b. Middle adulthood

c. Old age (senescence)

(a) Early adulthood

Is the period between 20 – 25 years of age

Physical and physiological changes during early adulthood

i. Growth has stopped, only maintenance of body parts take place

Example, repair of worn out cells, gain of body weight due to high deposition of fats.

ii. People are in their best physical conditions.

Example, they are very strong, energetic, have good memory capacity, sharp senses and stamina.

iii. Performance of the body system is very high.

iv. People are very ambitious and want to succeed. They work hard to meet their goals, for example to finish studies, get a job, start a family.

v. They have the desire to be socially independent.

(b) Middle adulthood

Is the period between 26 – 55 years of age.

Physical and physiological changes during middle adulthood

i. Initially, a person is still very strong and able to do tasks that require a lot of energy.

ii. The body system performance is still high.

In the late forties or early fifties, the rate of deterioration becomes significant.

iii. The ability to do tasks that require a lot of energy and high speed decrease, sharpness of vision decreases and memory loss may occur.

iv. Hair starts to turn grey and the skin starts to loose elasticity.

v. Women reach menopause and their desire to have sex is reduced.

x. OLD AGE (senescence)

Is a period between 56 years and above.

Physical and physiological Changes

1. The ability to focus on objects, smell and hear decreases.

2. Hair turns grey as a result of reduced production of hair pigment. Some men may develop a bald head.

3. Loss of memory due to death of brain cells.

4. Kidney functioning slows down and the frequency of urination increases.

5. Decreases blood flow to the brain and death of nerve cells.

6. Elasticity of the skin decreases hence. The skin gets looser and wrinkles develop.

7. Bones may become weak especially for those who have been taking food with less calcium in young age.

8. Men delay getting erection.

9. By the age of 70, about two thirds of taste buds in the month die, making a person feel like food in tasteless.

NB: The above features do not apply to all aged people. Healthy life style during young age may delay occurrence of the above features and make a person lead a normal life even in older age. – A healthy life style is achieved by eating healthy food, avoiding smoking, alcoholism, overeating, drug abuse and inactivity.

xi. DEATH

Is the end of life.

The cells and all body processes stop to function.

FACTORS AFFECTING THE RATE OF DETERIORATION OF THE HUMAN BODY

Factors affecting the rate of deterioration of the human body have been categorized into;

a. Psychological factors

b. Environmental factors

c. Genetical factors

(a) PSYCHOLOGICAL FACTORS

The following are psychological factors that affect the rate of deterioration of the human body:

i. Smoking

ii. Alcoholism

iii. Drug abuse

iv. Stress

v. Inactivity

(b) ENVIRONMENTAL FACTORS

The following are environmental factors that affect the rate of deterioration of the human body:

i. Poor diet

ii. Excessive noise

iii. Toxic chemicals and radiations

iv. Diseases and infections

(c) GENETICAL FACTORS

The following is genetic factor that affect the rate of deterioration of the human body:

(i) Werner’s syndrome

SMOKING

Smoking reduces life span by 12 years. Smokers suffer more illnesses such as cancer than nonsmokers. Smoking leads to premature balding, skin wrinkling and osteoporosis.

NB:

OSTEOPOROSIS

Is a condition in which bones are become thin and fragile, leading to fractures, stooped postures, breathing problems and back pain.

ALCOHOLISM

The ability to metabolize alcohol decrease with age. Prolonged use of alcohol leads to damage of the central nervous system and brain and increase the risk of heart stroke and breast cancer for women.

DRUG ABUSE

Drug abuse weakness the immune system and causes premature ageing. It thus reduces life span.

STRESS

Stress may cause heart problems and high blood pressure. It also causes impairment of the immune system, thus making a person sick often. Other problems that may result from stress are failure to sleep (insomnia), fatigue, headache and migraine.

INACTIVITY

Sedentary work and inactivity such as spending a long time watching TV or doing office work that involves sitting most of the time results in being overweight and its associated risks.

People who are inactive have more chances of developing health problem such as obesity and high blood pressure than those who are active.

POOR DIET

Poor diet includes both underfeeding and over-feeding. Under-feeding cause malnutrition which reduces life span while over-feeding leads to obesity and diabetes, obesity cause premature age.

DISEASES AND INFECTIONS

Pathogens produce toxins that accelerates deterioration. They also deprive our bodies the necessary nutrients needed for good health.

CHEMICAL AND RADIATIONS

Some chemicals such as those found in cosmetics, medicines, insecticides, pesticides, foodstuffs and sprays may have adverse effects in the human body.

These chemicals speed up deterioration or shorten life span.

Some radiations for example x-rays may affect our lives by killing body cells or causing deadly diseases like cancer.

GENETICAL FACTORS

A small number of individuals carry a defective gene that causes Werner syndrome. Werner’s syndrome is a very rare disease that causes premature ageing. It causes a 20- or 30-years old person may look several decades old.

SOCIO-CULTURAL FACTORS THAT AFFECT GROWTH AND DEVELOPMENT

The following are socio – cultural factors that affect growth and development

i. Traditional beliefs

ii. Poverty

iii. Religion

iv. Ignorance

TRADITIONAL BELIEFS

Some cultural practices may affect the growth and development in human. For example in some tribes pregnant women are not supposed to eat eggs, which contain proteins needed for growth and development of the unborn baby.

POVERTY

People having low income may fail to provide the basic needs for proper growth. Poor or insufficient diet and lack of medical care result into poor growth and even death especially at infancy.

RELIGION

Some religious sects prohibit certain groups of people from eating certain food. For example, Muslims do not eat pork on religious grounds. Some religious sects do not allow their followers to go for treatment in hospital resulting to poor health and even death.

IGNORANCE

Lack of knowledge about proper diet, proper medical care and education contribute to poor health. Most people do not know how to care for themselves, and do not know what is good and bad for them.

GROWTH AND DEVELOPMENT IN FLOWERING PLANTS

In most flowering plants growth starts when the seed begin to germinate.

In flowering plants, development starts with the growth of zygote into an embryo

SEED

Is a structure formed after the fertilization of an ovule.

A seed contains the embryo.

The embryo grows and develops into a mature plant which produces more seeds.

The embryo is made up of the plumule, radicle and cotyledons.

TYPES OF SEED

There are two types of seeds, namely:

A. Monocotyledonous seed – is a seed with one cotyledon. E.g. Maize, rice, millet, and wheat.

DIAGRAMS BELOW ARE LONGITUDINAL SECTION OF A MAIZE GRAIN

(a) External structure

(b) Internal structure

B. Dicotyledonous seed – is a seed with two cotyledons. E.g. Beans, peas and groundnuts.

DIAGRAMS BELOW ARE LONGITUDINAL SECTION OF A BEAN SEED

PARTS OF A SEED AND THEIR FUNCTION

A seed contains the following parts:

PART	FUNCTION
(i) Testa/ seed coat	Protects inner parts of the seed
(ii) Micropyle	Allows water and air to get in and out of the seed.
(iii) Hilum (a scar on the testa)		Point of attachment of seed to the fruit
(iv) Endosperm and cotyledon		Stores food for the seed
(v) Plumule		Develops into a shoot
(vi) Radicle		Develops into a root
(vii) Hypocotyl (the base of radicle)		Attaches radicle to cotyledon stalk
(viii) Epicotyl (the base of plumule)		Attaches plumule to cotyledon stalk
(ix) Coleoptile		Protects the tip of the plumule
(x) Coleorhiza		Protects the tip of the radicle

GERMINATION

Is the process by which the seed develops into seedling.

CHANGES WHICH OCCUR DURING SEED GERMINATION

i. The seed absorbs water through micropyle and enlarge.

ii. The testa bursts and the radicle emerges.

iii. Radicle continues to elongate and gives rise to many roots.

iv. Then the plumule emerges at this stage the young plant is called a seedling.

TYPES OF GERMINATION

There are two types of germination, namely:

i. Epigeal germination

ii. Hypogeal germination

(i) EPIGEAL GERMINATION

Is a type of germination in which the cotyledons are brought above the soil level.

In epigeal germination, the hypocotyl elongates rapidly raising cotyledons and the plumule above the soil.

It occurs in dicotyledonous plants such as beans, sunflower and in some monocotyledonous plants such as the onions.

Diagram below showing Epigeal germination

 

(ii) HYPOGEAL GERMINATION

Is a type of germination in which the cotyledons remain underground.

In hypogeal germination, the epicotyl elongates rapidly raising the plumule above the soil and leaving the cotyledon below the ground.

Hypogeal germination occurs in plants such as maize, pigeon peas, wheat, etc.

These seeds have large food reserved in their cotyledons

Diagram below showing hypogeal germination

CONDITION NECESSARY FOR GERMINATION

There are four conditions necessary for germination, namely:

i. Water

ii. Oxygen

iii. Optimum temperature

iv. Light

CONDITIONS	FUNCTION
WATER	–	It provides a suitable medium for enzymes to break down the stored food in the cotyledons or endosperm into suitable form.
	–	It hydrolyzes food substance into glucose.
	–	It is used to transport food materials between the cells.
	–	It softens the seed coat/testa so that it ruptures (bursts easily)
OXYGEN	–	It is necessary for respiration which provide energy required for the germination process.
TEMPERATURE	–	Optimum temperature activates the enzymes involved in the mobilization food reserves. Seeds will not germinate below 0℃ because low temperatures will inactivate the enzymes.
LIGHT	–	Some plant seeds need darkness while others need light in varying degrees

SEED DORMANCY

Is an inhibition of growth of an organism or part of it.

During seed dormancy the metabolic activities are usually very slow but sufficient to keep the cells alive.

IMPORTANCE OF SEED DORMANCY

i. Enables seed to survive for long time without depleting their food reserves.

ii. Enables the seed to survive adverse environmental conditions such as drought, extreme temperature and lack of food.

iii. Helps an organism to withstand unfavourable conditions such as drought.

iv. Allows time for dispersal of seeds by agents such water and wind.

CAUSES OF SEED DORMANCY

1. Nature of the testa

2. Presence of certain chemicals

3. Immature embryo

4. Presence of chemical inhibitors.

5. Lack of oxygen.

6. Lack of moisture (water).

7. Freezing of seed

NATURE OF THE TESTA

Some seeds the teste may be impermeable to oxygen and water. In such seeds time is required before the teste becomes permeable. The teste may also be hard – preventing the radicle and plumule form emerging.

PRESENCE OF CERTAIN CHEMICALS

Certain chemicals present in either the seed or fruit are known to prevent seed germination. These chemicals are removed by leaching.

IMMATURE EMBRYO

Some seeds will not germinate immediately after harvest. It has been found out that at that time embryos are not fully developed. Such seeds have to go to be stored for some time so that the embryo develop fully. The period is called after-ripening.

WAYS OF BREAKING SEED DORMANCY

1. Provide water

2. Provide air

3. Provide suitable temperature

4. Ensure seed embryo is mature

5. Ensure growth hormones such as gibberellins are present.

6. Inactivate the germination inhibitors

7. Burn gently some seeds such as jacaranda which have hard testa to burst open the seed coat.

DISADVANTAGES OF DORMANCY

i. Seed have to be produced in big number.

ii. Plants with dormant seeds do not reproduce as quick as others.

iii. Seed may be exposed to unfavourable conditions for long time i.e many seeds get spoiled

SEED VIABILITY

Is the ability of a seed to germinate

The seed which retains its capability to germinate is known as viable

Only alive and healthy seeds with mature embryo germinate.

Seeds have been stored for a very long time may lose their viability/

FACTORS AFFECT THE VIABILITY OF SEEDS

i. Seed maturity.

ii. Temperature

iii. Availability of moisture

iv. Nature of a testa

v. Storage condition.

vi. Food stores

GROWTH REGIONS OF A SEEDLING

In plants growth and development take place in certain localized regions called meristems.

MERISTEMS

Are regions in plants where growth and development take place

The main meristems are located at the tip of the shoot and tip of the root.

Active cell division and cell differentiation occur in the meristems.

Diagram of longitudinal section of a root tip showing the growth regions of a root

Diagram of longitudinal section of a shoot showing growth regions of a shoot

TYPES OF MERISTEMS

There are three types of meristems, namely:

i. Apical meristems

ii. Lateral meristems

iii. Intercalary meristems

i. APICAL MERISTEMS

Are meristematic tissues located at the tip of the shoots and tip of the roots.

Apical meristems bring about an increase in length and height of roots and shoots.

Apical meristems are made up of very dividing cells called meristematic cells.

ii. LATERAL MERISTEMS

Are meristematic tissues that give rise to branches of shoot.

Lateral meristems bring about the increase in growth of the shoots and roots.

iii. INTERCALARY MERISTEMS

Are meristematic tissues that bring about internode elongation

Intercalary meristems are located in the axillary buds

The part of a stern between one node and the next is called internode

PRIMARY AND SECONDARY GROWTH IN PLANTS

I. PRIMARY GROWTH

Is the increase in length of the shoot and root

Primary growth leads to increase in length of the plant

The increase in length is brought about by cell division, cell elongation and cell differentiation.

Meristematic cells in the root and shoot tips undergo cell division to produce new cells.

These cells undergo specialization to form primary tissues.

Primary tissue leads to elongation of the plant shoots and roots.

II. SECONDARY GROWTH

Is the increase in thickness (girth) of woody stems and roots

Secondary growth leads to increase in plant width.

It does not occur in herbaceous annual and biennial plants which only live for one or two years.

Secondary growth is caused by meristematic cells located in the vascular cambium.