The Development of Seed and Fruit After Fertilisation

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THE DEVELOPMENT

OF SEED AND FRUIT

AFTER

FERTILISATION



After fertilisation,

The zygote multiplies by mitosis to form anembryo

Embryo then divides and differentiates to

form a radicle, plumule and cotyledon(s) Integuments that surround the embryo sac

formed the seed coat (pericarp), the outer covering of the seed

Triploid endosperm cell divides rapidly and

develops into the endosperm Endosperm provides nutrients to the

growing embryo



4.6Growth inMulticellular Organisms



Growth: The Definition of

Growth in Human Being Takes place in an organism from a

zygote until adulthood

Irreversible process which results inincreases in the size, body mass and

number of cells

Quantitative changes such as increase

in solid matter, dry mass and the

amount of cytoplasm



Development

Refers to the change in shape, function

and degree or complexity that

accompany growth Involves qualitative changes

associated with differentiation and

specialistaion



The process of Growth can

be divided into three stages:- Cell division stage

Cell enlargement stage

Cell differentiation stage



Cell division stage

Number of cells in organisms

increases

Mitosis Reproduces in geometric progression

E.g 2 to 4, 4 to 8«.



Cell enlargement stage

Size and volume of cells in an

organism increase through the intake

of water and other necessary

substance

In plants, it involves vacuolation



Cell Differentiation Stage

Cells become specialised

Permanent cells with specific functions

E.g epidermis, xylem and phloem inplants, neurones and specific types of

blood cells



Growth in plants

Stages of development in growth can

be distinctly observed in the shoot tip

and root tip of plant

Apex of a shoot/root can be divided

into three growth zones:

(a) The zone of cell division

(b) The zone of cell elongation

(c) The zone of cell differentiation



PRIMARY GROWTH IN PLANTS



Growth in Plants

Growth in the mentioned zones

constitutes the primary growth of a

plant



4.7 The Growth Curve

Can be estimated by measuring certain

parameters such as length, height,

volume, fresh mass and dry mass



The Sigmoid Growth Curve of

An Organism Growth curve is S-shaped and is

known as sigmoid curve



The Phases Involved:-

Lag phase

Rapid growth phase (Exponential

phase) Slow growth phase

Stationary phase

Senescence phase



The growth curve of Humans

There are two phases of rapid

growth:-

(a) Early infancy(b) Adolescence

Between these two phases, there is a

period of steady growth



The Growth Curve of an

Insect Insect has hard, inflexible external skeleton

Insect undergoes moulting periodically

during growth

Moulting or ecdysis is the process of

removing an old skeleton and replacing it

with a new larger one

When the length of an insect is plottedagainst time, it shows an intermittent growth



MOLTING IN CICADA



The Growth Curve of an

Insect («continued) Shaped like a series of steps

Horizontal parts indicates zero growth

The insect stops growing

Five vertical lines of the curve are suddengrowth spurts

Nymphs undergo ecdysis

An insect undergoes ecdysis several timesbefore it reaches the adult phase

Each stage between the moultings is calledan instar



How Ecdysis Occurs

A new exoskeleton forms below the oldskeleton

Old skeleton softens and its essentialresources are digested and reabsorbedinto the new skeleton

Old skeleton splits and is discarded

The insect enlarges its body volumesby swallowing air or liquid until newcuticle hardens

The Development of Seed and Fruit After Fertilisation

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