•Plants are everywhere. However how well do we know them? Firstly, how do they different from animals and us? Yes, they make food themselves through photosynthesis. What do they need in order to carry out photosynthesis?

•Do plants have any circulatory system like us to carry food and water to other parts of the plants? How do they reproduce? Do plants response to stimuli?

Plants

a.Green plants are producers.b.Only green plants possess the amazing ability of trapping solar energy to produce food.c.Photosynthesis is the process in which green plants absorb solar energy to make food from carbon dioxide and water.

Photosynthesis

d. Oxygen is released as a by- product.e. Chlorophyll is the green pigment present in the leaves that

can absorb sunlight.f. The glucose produced during photosynthesis is then

converted into starch. Starch is stored in the stems, fruits or roots of plants.

Photosynthesis can be represented by the following equation:

Water + carbon dioxide sunlight glucose + oxygen chlorophyll

Requirements of photosynthesis

1. The necessary factors for photosynthesis:a.Sunlightb.Chlorophyllc.Waterd.Carbon dioxide

2. Photosynthesis will not take place if any one of these factors is absent.3. We should test for the presence of starch in leaves to determine whether photosynthesis has taken place in a plant.

Sunlight

Water

Carbon dioxide

Chlorophyll

•Testing for the presence of starch in leaves

1. Below are the steps to test for the presence of starch in a leaf.

immerse a leaf in boiling water for a minute to soften and break the cells.

transfer the boiled leaf into a boiling tube containing alcohol . Place the boiling tube in a water bath for a few minutes to decolourise the leaf. remove the leaf and put it back into the hot water for a few seconds to soften the leaf.

1. Spread the leaf into a white tile. Add a few drops of iodine solution to test for the presence of starch.

2. The presence of starch can be tested using iodine solution after the chlorophyll of the leaf is removed.

3. The areas containing starch will be stained blue-black when iodine solution is added.

-Photosynthesis is an important process. This process manufactures food for all organisms on Earth.

-All organisms need food but only green plants are capable of trapping solar energy to manufacture food from simple substances.

-All other organisms, animals or non- green plants, are directly or indirectly dependent on green plants for food.

The importance of photosynthesis

- Green plants start the food chain and they are the producers in any ecosystem.

- Therefore, photosynthesis is an important process that provides food for all organisms.

- Photosynthesis replaces the oxygen that is used up in the following process.

a. Respiration of living things.b. Combustion of fuelc. Decomposition of dead plants and animal

material.

- On the other hand, photosynthesis absorb carbon dioxide in the atmosphere that is given out during respiration, combustion and decomposition.

- The concentration of oxygen and carbon dioxide in the atmosphere are maintained by the oxygen and carbon cycles.

- Therefore, photosynthesis and respiration are important in maintaining a balanced level of oxygen and carbon dioxide in the atmosphere. These processes will lead to a balanced ecosystem.

The transport system in plants

•Wilting-Non-woody plants depend on the water stored in the cells of the stemfor support.

-Wilting occurs in non-woody plants when water loss through the aerial parts of the plants exceeds water absorption by the roots.

-Cells in the plants lose their turgidity stiffness) and the plant droops.

-Wilting can be important to the plants because the leaf surfaces are removed from the direct rays of the Sun and the stomata close. Water lose from the plants will be reduced.

-Normally, a plant which has wilted will remain in this condition until evening.

-In the evening, water absorption exceeds water loss and the cells become turgid again.

•Transpiration

-Transpiration is the evaporation of water from the aerial parts of plants.

-90% of the water absorbed by the roots is lost by evaporation from the surfaces of cells in the leaves and subsequent diffusion of water vapour through the stomata. 9% is lost through the cuticle. The remaining 1% is used for photosynthesis.

•Stomata

-Stomata are pores in the epidermis of the leaves and stems.

-A pair of bean-shaped guard cells bound each stomata.

Surfaces view of a stoma

- In most dicotyledons, stomata appear only in the lower epidermis of the leaf.

-In monocotyledons, stomata are found on both sides of the leaf.

-Most stomata open during the dday and close at night.

-The main function of the stomata is to allow gases to diffuse in and out the leaf. During photosynthesis, carbon dioxide diffuses from the atmosphere into the leaf and oxygen diffuses out from the leaf into the atmosphere.

- When the stomata open, water vapour is released to the surroundings through the stomata by transpiration. However, the stomata will close when the transpiration exceeds water absorption.

Factors that affect the rate of transpiration

•Light – light stimulate the opening of stomata and consequently increases transpiration.

•Temperature- water molecules move faster in warm air, hence the rate of transpiration is increased.

•Relative humidity – the rate of water loss depends on the difference in the concentration of water molecules in the leaf and in the atmosphere. High relative humidity reduces water loss.

•Wind speed – an increase in wind speed increases the rate of transpiration because the movement of air carries away the water vapour from the stomata.

•Water availability – short supply of water causes the plant to wilt and the stomata to close. This reduces the rate of transpiration.

•Altitude – in the mountains, the atmospheric pressure decreases sufficiently to cause an increase in the rate of transpiration.

The roles of transpiration

•The pulling force developed by transpiration provides the pathway through which water and minerals are transported in the plant.

•Evaporation from the leaf surface has a cooling effect which helps to prevent the heat of direct sunlight from damaging the delicate cells.

Vascular tissues of plant

•The vascular tissues are concerned with transport and are functionally equivalent to the circulator system of mammals

•The two types of vascular tissues are called xylem and ploem.

•Xylem a. The main function of the xylem is to transport water and mineral salts from the roots to the stem and leaves.

b. Xylem forms wood in shrubs and trees. Therefore, xylem provides support to the plants

c. Xylem consists mainly of vessels, which are elongated tubes with thick walls. The walls are strengthened with a substance called lignin. Xylem vessels are dead structures without protoplasmic contents and transverse walls.

Xylem vessels

•Phloema.Phloem transports synthesised food substances from one part of the plant to another.

b.Phloem consists mainly of sieve tubes. Sieve tubes are living cells without nucleus. The walls of sieve tubes are composed largely of cellulose. The transverse walls of sieve tubes are perforated by pores and are called sieve plates.

c.Each sieve tube cell has a companion cell beside it.

Phloem Cells

The sexual reproductive system of flowering plants

Structure of flower•Flowers are the sexual reproductive organs of plants.•The flower sits on the expanded end of a flower stalk called the receptacle.•The outermost parts of the flower are the sepals. The sepals are usually small, green and leafy-like.•The petals maybe coloured, scented and sometimes fused into a tube.•The female part of the flower is called the stamen.Each stamen consists of an anther at the end of a stalk-like filament. The anther consistspollen grains.

•The female part of the flower is called the pistil or carpel. The pistil consists of stigma style ovary and ovules.

There are two types of flowers

a. Unisexual flowers contain either the stamens (male flowers) or the pistils (female flowers)

Example of unisexual flower

b. Bisexual flowers contain both the stamens and the pistils

Example of bisexual flowers

•Pollen grains come in a diversity of shape and sizes. The outer wall of each pollen grain has a pattern characteristics of each species.

Pollen grains from (a) grass, (b) rose an(c ) hibiscus plant

•Pollen grains are carries of the male gametes of the plants.•The ovules are formed in the ovary and they contain the female gametes

a.The cross section b. the longitudinal sectionOvary

Parts of flowers Function

Receptacle Supports the flower

Sepals Supports the young flower when it is in the budding stage

Petals Attract animal pollinators through their colour and scent

Stigma Receive pollen grains

Style Connects the stigma to the ovary

Ovary

Protects the ovules. After fertilization, the ovary develops into a fruit to protect the seed

Ovule

Contains the female gamete (egg cell). After fertilization, the ovule developes into a seed.

Anther Produce male gametes (in pollen grains)

Filament Supports the anther

Pollination

•Pollination is the transfer of pollen grains from anthers to stigmas.•Pollen grains cannot move independently and their main means of transport is by agents of pollination.•The chief agents of pollination are wind and insects but birds, bats, snails and even water may carry pollen grains from one flower to another. The chief insect pollinators are bees and butterflies.

Structure of an insect- pollinated flower

Structure of a wind-pollinated flower

Differences between insect-pollinated and wind- pollinated flowers

Insect- pollinated

•Large and conspicuous

•Brightly couloured

•Present

•Scented

Wind- pollinated

•Small and inconspicuous

•Greenish and dull couloured

•Absent

•Absent

Size

Petals

Nectaries

Scent

Insect- pollinated

•Inside flower, where insect have to brush past them to reach the nectaries.

•Small sticky and remain inside the flower.

•Quite large quantities, larger, heavier, and rough – surfaced.

Wind- pollinated

•Dangled outside flower, where they catch the wind.

•Large, feathery and hang outside the flower.

•Very large quantities, small, light and smooth

Anthers

Stigmas

Pollen grains

•Self pollination is the transfer of pollen grains from the anther to the stigma of the same flower, or from the anther to the stigma of a different flower in the same plant.•Cross pollination is the transfer of pollen grains from the anther of one plant to the stigma of another plant of the same species.

(a)Self- pollination (b) Cross- pollination

Similarity and differences between self-pollination and cross- pollination

Self- pollination and cross- pollination are both involve the transfer of pollen grains from the anther

to the stigma.

Differences

Self- pollination Cross- pollination

•Involves pollen grains and stigmas from the same flowers, or from different flowers of the same plant.

•Involves pollen grains and stigmas from flowers of different plants of the same species.

Self- pollination Cross- pollination

•Offspring have the genetic materials of only one parent. It is form of inbreeding and results in less varied offspring.

•Can occur even before the flower opens fully.

•Less common from pollination.

•Offspring have the genetic materials of two parents. This results in increased variability in the offspring and greater adaptability to new environments

•Depends on agents of pollination

More common form of pollination.

The advantages of cross- pollination

•Cross- pollination has the distinct disadvantage of providing more genetic variations of the offspring.•More variation will help the offspring to survive in a changing environment.

Use of cross- pollination in agriculture

•For centuries, farmers have been trying to cultivate new varieties of crops through cross breeding of closely related plants.•The main aim of cross breeding is to produce offspring with desirable characteristics of each parent.

•Cross breeding can be achieved through cross- pollination. For example, the pollen grains of a high yielding variety of rice are artificially placed on the stigmas of another variety of rice that has resistance to diseases. Cross pollination might produce offspring that are both disease resistant and high yielding.

•The tenera variety of oil palm is produced by cross- pollination the dura variety with the pisifera variety.

Cross- pollinating the dura variety with the pisifera variety yields the tenera variety

The development of fruits and seeds in plants

Fertilization in plants•After pollination, the male gamete inside the pollen grain on the stigma still has not reached the female gamete because the female gamete is inside the ovule and the ovule is inside the ovary.•Sugary secretion of the stigma causes the pollen grain to germinite and produce a pollen tube.•The pollen tube grows down through the style and enters the ovule through a tiny hole called the micropyle.•The male gamete in the pollen tube fuses with the female gamete (egg) to form a zygote. this process is called fertilization.

Fertilization in plants

•One pollen grain can only fertilizes one ovule.•If there are many ovules in the ovary, then many pollen grains will be needed to fertilize them all.

Formation of fruits and seeds

•Once the ovule have been fertilized, the sepals, petals and stamens wither and fall off.•The fertilized ovule develops into a seed and the ovary as a whole develops into the fruit.•The number of seeds in a fruit depends in how many ovules there were in the ovary and how many were fertilized.

•The wall of the fruit called the pericarp develops from the wall of the ovary.•As the fruit matures, the pericarp may become hard and dry (e.g. sweet pea, castor oil) or juicy and fleshy (e.g. mango and tomato). Juicy fruits are called succulent fruits.

(a)Fruit of sweet pea plant (b)fruit of mango plant

The germination of seeds

Structure of a seed•Seeds have protective covering called the testa.•The zygote develops into an embryo which consists of:a.A young root called the radicle.b.A young shoot called plumule,c.One or two seed leaves called cotyledons•Seeds with two cotyledons are called dicotyledonous seeds ( e.g. soya bean and broad bean) and seed with one cotyledon are called monocotyledonous seeds (e.g. paddy and wheat).

•Food for the embryo is deposited either inside the cotyledons or in the endosperm.•On the testa is a scar called the hilum, which is the point where the seed is attached to the ovary wall.•The micropyle lies above the hilum.•The fruit wall called the pericarp protects the seeds.

The maize grain