TOPIC 1.GROWTH

GROWTH

Growth is an irrevessible increase/permanent increase in size and mass of an organisim

Development

Development are changes in the complexity/structure of an organism

·         It involves differentation and formation of various tissue that perform specialized functions.

·         Growth is quantitative (can be measured: height, mass,volume 

·         Development is qualitative (can’t be measured)

·         The growth and development of a young organism into adult involves cell division (multiplication of one cell into two, two into four and four into eight ect. 

·         The newly formed daughter cell have the same composition as the parent cell although they may be smaller, late cells enlarge to the adult size and even divide again.

       

CONCEPT OF GROWTH

Growth can be measured using a curve. A growth curve is a graph obtained when data collected during stages of growth is plotted against the time.

A growth curve shows growth pattern of the organism. In most organisms growth pattern is almost the same where by first shows slow then speeds up and finally slows down.

This pattern gives an S-shaped curve known as sigmoid curve.

Lag phase

Lag phase is a period when the rate of growth is very slow during the stage the number of cell dividing through mitosis are few

Log phase /exponential phase

This phase involves very rapid growth where by the number of cell division is higher than the dead face

Linear growth /declarating phase.

This phase involves the decline in the rate of growth as maturity is approached the rate of cell division decrease.

Stationary phase/plateau phase

This phase marks the period of no further changes in the size of the organism the organism has sustained maturity new cells are formed only to replace those worn out or dead cells

Measurement of growth

1.      Measuring the length parts used to measure growth leaves, stems, internodes etc.

2.      Measuring weight

3.      Measuring area

MITOSIS AND GROWTH

Mitosis is a type of cell division which increases the number of cells which bring about growth.

·         It results into two identical daughter nucles with a diploid number of chromosomes

Phases of Mitosis

·         It consists of 5 phases namely

§  Interphase

§  Prophase

§  Metaphase

§  Anaphase

§  Telophase

 1. INTERPHASE

o    This is the phase were the cell is engaged in many cellular activities to prepare for the cell division.

o    The entire proces takes about 1hour. It is incorrectly referred to as resting phase.

o    The following are observed

§  DNA replicates

§  Chromosomes apper

§  Centriole replicates

§  Energy is synthesised and stored

 

2. PROPHASE

o    In this stage centrioles separate and migrate to opposite cell’s poles.

o    Chromosomes become visible, thicken and shorten

o    Each chromosome divides into two along its length replication except at the centromere. Chromosomes now called chromatids.

o    The nucleas membrane and nucleolus gradually disappears.

o    A network of fibres starts to form

 

.3. METAPHASE

·         The chromatids move to the centre of cell.

·         The chromatids become arranged and attached to spindle fibres by centromeres.

·         The chromatids draw apart at the centromere region

 

                       4. ANAPHASE

·         In this stage, after the sister chromatids part company, they migrate to the apposite poles of the spindle, the centromere leading it.

·         Chromatids reach their destination towards the poles of the spindle. Now chromatids are called chromosomes.

 

             5. TELOPHASE

·         In early telophase, the spindle fibres disappear,

·         A nuclear membrane is formed enclosing the newly formed chromosomes.

·         At this stage, in animal cells, the cell starts to construct across the middle into two new cells.

·         In plant cells a cell wall is formed across the middle of the cell

 

SYTOKINESIS

            This is the division of the sytoplasm

·         It is through the formation of a new cell wall in plant cell or the constriction of the animal cell.

SIGNIFICANCE OF MITOSIS

·         It is the basis of asexual reproduction 

·         It maintains the diploid state of the organism

·         It is the basis of growth i.e it brings about growth in terms of increase in number of cells.

·         It help to recovery of dead worn out cell

DIFFERENCE BETWEEN MEIOSIS AND MITOSIS

SN	MEIOSIS	MITOSIS
	Occurs in reproductive cells to form gameters	Occurs in body cells during grow and tissue repair (somatic cell)
	Gametes fuse to form a zygote	New cells do not fuse to form a zygote
	Variation occurs through chromosomes recombination	No variation, all are like parents.
	Takes place in two phases to complete	Take place in one phase to complete a successful cell division
	New formed daughter cells are in haploid state	Newly formed daughter cells are in diploid state

THE PROCESS OF GROWTH

It in volves the following: -

§  Assimilation

§  Cell division

§  Cell expansion

1. ASSIMILATION

·         Is the incorporation of the materials absorbed from the surrounding into the cell metabolism (food and gases)

·         From this procces cell get raw material for energy production.

·         Energy is used in the next stage

                     2. CELL DIVISION

·         This is the division of cell nucleas and cytoplasm

·         It results in increase in the number of cells (growth)

                     3. CELL EXPANSION

·         Cell increase in size when they absorb water by osmosis. The cell take in water in their vacoules and expand.

GROWTH AND DEVELOPMENT IN ANIMALS

TYPES OF GROWTH

1.      ALLOMETRIC GROWTH

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

2.      DIFFUSE GROWTH

Is the type of growth where by growth occurs all over the body of an organism

3.      LOCALIZED GROWTH

Is the type of growth where by growth occurs in certain region e.g: In plants at the tip and shoots of the roots. Tips are called maristems

4.      INTERMITTENT GROWTH

Is the type of growth in intropods which growth takes place isnseries of stages called instars. Example in insects an egg hatch into larva then develops into a pupae, finally an adult.

5.      ISOMETRIC GROWTH

Is the type of growth where by all body organs grow at the same rate e.g in a fish.

6.      DETERMINATE GROWTH

This growth is seen in individuals which stop growing when certain body size or age is attained e.g. in mammals, birds, animals, plant

7.      INDETERMINATE GROWTH

Is the type of growth shown by organisms that do not stop to grow i.e organism show increasing growth

Example in shrubs, corals, fish, reptilires

GROWTH AND DEVELOPMENT IN ANIMALS

Growth in arthropods

At arthropods show discontinuous growth. This is a type of growth characterized by a number of periods of rapid growth followed by periods of little or no growth.

Some arthropods they show incomplete life style also there some arthropods show complete life cycle are known as polometabolous I.e.Butter flies, house flies. Bittles, etc.

               INTERMITTENT GROWTH

This is the type of growth that occurs in a series of stages in arthropods. These series of stages show sudden changes in weight or length measured over weeks or months.

Each stage is known as instars. All arthropods have an exo –skeleton which prevents overall growth of the body.

Therefore they have to shade their exo skeleton so that they can grow this is known as moulting or ecoysis.

At the final shading of the exoskeleton the insect under goes full development and the wings expand enabling flight