PLANTS

Plants are living things. As living things, plants show characteristics shown by other living things.

Characteristic of living things

1. Plants grow.
2. They reproduce through seeds, fruits and vegetative reproduction
3. Plants move by growing either upwards or sideways. Plants move towards light by growing and they even make curves in order to reach things like water and sunlight
4. They respire: respiration is the burning of food in the body to produce energy.
5. Plants feed by taking in nutrients like carbon dioxide from the air,
   water and mineral salts from the soil and make their food by the processes called photosynthesis
6. Plants remove wastes. They excrete. During the day, plants remove oxygen
   as a waste product in the process of photosynthesis. At night, plants
   release carbon dioxide as waste. The stomata are very important in the
   removal of wastes from plants.
7. Plants respond to changes in the environment, for example, they
   respond to shortage of water by their roots growing towards the source of When it is too hot, plants close their stoma (stomata – singular) so that they don’t lose too much water

 Uses of plants

• Food
• Shelter
• Building material
• Medicine
• Wind breakers
• Decoration and beauty

Parts of a plant

The parts of a plant include:

• Roots
• Bud
• Flowers
• Leaves
• Stem
• Fruit

Dicotyledonous plant, e.g. bean

Monocotyledonous plant, e.g. maize

Differences between monocotyledonous and dicotyledonous plants

Monocotyledonous plant	Dicotyledonous plant
One seed leaf or cotyledon	Two seed leafs
Leaves with parallel veins	Leaves with network veins
Has fibrous root system	Has tap root system
Examples are maize, millet, banana	Examples  are beans, mango, avocado tree

 

The root

Roots of a plant are found below the ground (in the soil).

Functions of the root

1. To anchor the plant firmly in the soil,
2. To absorb water and nutrients from the soil and pass them to the stem.

• In some plants such as carrots and cassava, the roots are used to store

1. To help in the taking in of air by water plants tike the mangrove. These roots are called breathing roots.
2. Prop root offer extra support

Taproot

The tap root is the main root which grows from the radicle and continues to grow bigger than its branches. It grows vertically down into the soil, producing smaller side branches.

Most dicotyledonous plants have this type of root. The best example is the carrot.

Fibrous root

Fibrous roots have no main root. Instead all the roots grow to almost the same size. The roots grow from the base of the stem and spread into the soil.

 Adventitious Roots

These are roots that arise from plant organs such stem, leaves other than roots

The stem

The stem performs the following functions:

1. It supports the other parts of the plant (leaves, flowers and fruits).
2. It helps in transporting water and dissolved nutrients from the roots to the other parts of the plant.

• Transports food that is made in the leaves to the roots for storage.

1. Stores food in plants like sugarcane.

The leaves

Leaves are the main photosynthetic organs of the plant

Functions of the leaves

1. Carry out photosynthesis with subsequent production of organic materials
2. Carry out gaseous exchange through the stomata
3. Transpiration takes place mainly through the leaves resulting in the cooling of plant and absorption of mineral salts and water
4. Some leaves such as those of peas are modified by tendrils for support.
5. Some leaves such as for bryophyllum are modified for vegetative reproduction
6. Some leaves are colored to attract pollinators.

Simple and compound leaves

Simple leaves have a single blade undivided lamina while compound leaves have their lamina divided into leaflets.

 

 The flower

This is the reproductive part of the plant.

Parts of the flower are:

6. Petal are colored and have scent that to attract insect for pollination. Petals are collectively called corolla
7. Sepals are often small and green. Sepals protect the young flower when in bud. Sepals are collectively called calyx.
8. The stamen is the male part of the flower. It is made of the filament and anther. The anther produces pollen grains (the male sex cells). The pollen grains are held in pollen sacs, in the anther.
9. The pistil is the female part of the flower. It is made of the stigma, the style and the ovary. The ovules (the female sex cells) are produced and held inside the ovary. The style is the tube that connects the stigma to the ovary. The stigma receives the pollen.
10. The nectary is the part of the flower that produces nectar. The nectary is located near the ovary.

Pollination

Pollination is the transfer of pollen grains from the anthers to the stigma of the same type of flower. There are two types of pollination:-

Self-pollination occurs when pollen from the anthers of a flower are transferred to the stigma of the same flower or a flower of the same plant.

Cross pollination occurs when pollen from the anthers of one flower are transferred to the stigma of a flower on another plant of the same type.

 

Agents of pollination

These are   the   things   that   help   in pollination.  They include

Wind

Insects

Water

Differences  between wind and insect pollinated flowers

Wind pollinated flowers	Insect pollinated flowers
Have small dull flowers	Have large and brightly colored flowers
Have no nectar and no scent	Produce nectar and often have a strong scent
The stigma below the anthers	Stigma above the anthers
Produce small and smooth pollen	Produce large sticky pollen
Produce pollen grains in abundance	Produce few pollen grains

 

Fertilization

This is the fusion or joining of the male and the female gametes (Sex cells of the plants). During pollination, the pollen grain lands on the stigma. The pollen grains then start to germinate producing a pollen tube. The pollen tube grows into and through the style into the ovary. The pollens then move through the pollen tube to the ovary where they are released to join the ovules. When the pollens and the ovules (male and female sex cells) fuse, then fertilization takes place.

Changes after fertilization

1. The fertilized ovule becomes a seed containing an embryo.
2. The ovule wall becomes the testa or seed coat.
3. The ovary grows to become a
4. The ovary wall becomes the pericarp or fruit wall.
5. The petals, sepal, anthers withers and dies.

The seed

The seed is the fertilized ovule containing the embryo. The embryo is made up of a plumule (grows to be the shoot) and a radicle (grows to be the root). The embryo is usually covered by one or two cotyledons, which are stored food for the embryo (the tiny plant in the seed). On the outside of the seed there is a scar called hilum, where the seed was attached to the fruit wall, and a small hole called the micropyle.

The bean seed has two cotyledons. The maize seed is actually a fruit and it contains one cotyledon, which is small compared to that of the bean. The role of the cotyledon in maize is to transfer food to the embryo. It stores food in the endosperm.

Plants that produce seeds with one cotyledon are called monocotyledonous plants. Examples of monocotyledons are maize, barley, wheat, rice and millet.

Plants that produce seeds with two cotyledons are called dicotyledonous plants. Examples of dicotyledonous plants are groundnuts, beans and castor oil.

Differences between seeds and fruits

Seed

• Contains the embryo and its food store
• Can germinate   under   favorable conditions
• Has a  scar   (hilum)   where   it  was attached to the fruit wall
• Has a micropyle (a tiny hole for taking in water during germination)

Fruit

• Contains seeds in it
• The seeds  germinate   after   being released from the fruit
• Has two scars:  one where  it was attached to the flower stalk and the other where it was attached to the style
• Does not have a micropyle.

 

Germination

This is the growth of a plant from a seed.

Factors that favor germination

• water
• Warmth
• oxygen

 

Types of germination

There are two types of germination namely:

Epigeal germination – the cotyledons are pushed above the ground when the seed germinates for example in beans and castor oil.

Hypogeal germination – the cotyledons remain below the ground when the seed germinates for example in maize, grasses and onions.

Seed Dormancy

Is the state in which a seed that is viable will not germinate even if the conditions that are necessary for germination are provided?

Dormant seed are usually dry, their metabolic activity is much reduced and they respire anaerobically.

Importance of seed dormancy

• Seed are able to withstand adverse external conditions such as very cold or very dry weather.
• It allows seed and fruits to disperse

Causes of seed dormancy

The main factors that causes the seed dormancy are:

1. Seed coats impermeable to water:.
2. Seed coat impermeable to oxygen:
3. Immaturity of the embryo:

Conifers

These are seed bearing non flowering plant. They bear naked seeds in cone instead of flowers.

 Fern, liverwort, moss

They are green non flowering plants.

They make their food by photosynthesis

They reproduce by production of spores

Spore are tiny structures that can grow into a new plant under favorable conditions

Fern, liverwort, moss are producers in a food chain

Mushrooms and moulds

They are classified as kingdom Fungi

They lack chlorophyll

They are saprophytes because they feed on dead decomposing organic matter

They reproduce by production of spores. Mushroom produce spores in the gills while moulds produce spores in the

Mushroom and moulds are decomposers in a food chain. They decompose and recycle nutrients in the environment.

Uses of mushrooms

Food

Medicine

Disadvantages

rot food

some are poisonous

Caring for plants

Plants are cared for through

1. Land preparation

This includes clearing land, diging, planting and fencing, watering and weeding

 (a)       Clearing of the land

A tool called a panga or a slasher is used to clear the land by cutting the remains of the previous crop or grass or bush. Some people then burn the resulting trash but burning is not a good practice because some nutrients are lost. Clearing also includes removing stones and other rocks from the piece of land.

(b) Digging or ploughing

If the plot is small, human labour is used but if it is a big piece of land, an ox-plough or tractor can be used for ploughing. Ploughing is done in order to:

• uproot and kill the weeds,
• expose and kill some crop pests that may be in the previous crop remains or on the weeds and
• Make the soil loose by breaking the hard lumps to allow plant roots to easily penetrate the land.

2. Fencing

Plants must be protected from being damaged by animals. To do this we should put a fence around the plot to avoid crop damage.

3. Planting

After land preparation, the seeds are planted. Apart from seeds, the other materials that can be planted are cuttings (for example, sugar cane and kales), tubers (irish potato), rhizomes (grasses), suckers (banana and sisal) and splits (pyrethrum).

4. Watering

Watering may be necessary during dry weather to enable crops grow well

5. Weeding

Weeding is removal of unwanted plants from the garden

Example of weeds include

What effects do weeds have on crops?
Weeds are bad because:

• They compete with plants for nutrients
• Carry diseases or disease causing organisms

 

Pests

These are destructive insects or other animal that attacks crops

Types of pests

There are two types of pests, namely:

Field pests which are

• Cutworm
• Aphid
• Maize
• Weaverbird
• 

Storage pests

Storage pests are the pests that attack the harvested crops when in storage. Examples of storage pests are weevil, termites and rodents

Effects of pests on crops

Pests affect crops in the following ways:

1. i) They lower or reduce harvest by competing with crops for nutrients
2. ii) Reduced quality of produce.

iii) Pests that suck plant juices transmit diseases from unhealthy plants to healthy plants.

 

Controlling pests

To eliminate or reduce wastage of crops and improve harvest, pests must be controlled. The methods of controlling pests include:

1. Trapping:This method can be applied for rodents and birds in food storage sheds.
2. Handpicking: Insects like weevils can be removed by hand.
3. Scaring: using noise or scare crow
4. Weeding
5. Spraying using insecticie
6. Pruning : removing unhealthy branches and leaves

Crop diseases

Signs of an unhealthy crop or diseased crop

• has curled leaves
• Shows discoloration of some parts such as its leaves, stems and ears has spots or streaks of colour. The color is different from the colour of its leaves or stem when it is normal. For example, yellow on green leaves.
• It may appear wilted, with the leaves
  drooping
• May have stunted growth. It may be smaller than other similar crops of its age.

Effects of crop diseases

The effects of diseases on crops may be:

• Less or reduced yield of harvest
• The quality of the produce is lower or poorer
• Lower quality of crop produce may lower the market value of the crop and reduce the farmer’s income
• The crop may die.

 

Type of crops

1. Food crops include

• Cereals – wheat and maize,
• Legumes – peas and beans,
• Vegetables – cabbages and kales,
• Fruits – oranges and mangoes and
• Tuber crops – yams and cassavas.

2. Cash crops include: coffee. Cocoa, sisal, cotton

 

 

Plant storage parts include

Root tubers – these include carrots, cassava and sweet potatoes. They store their food in the swollen root.

Bulbs – examples of bulbs are the onion which stores its food underground. The bulb contains the roots, flat stem and thick fleshy leaves.

 

Stem tubers – an example is the irish potato. It is the swollen part of the stem that is found under the ground and it contains several buds (eyes).

Rhizomes – an example is the ginger. It is an underground stem that grows horizontally.

Habitats

A habitat is a place where a living organism lives or grows.

Interdependence between plants and animals

The interdependence can also be between plants and animals. Animals and plants depend on each other for various reasons. These reasons include:

1. Plants depend on animal for

• carbon dioxide for photosynthesis
• manure from their dropping
• pollination
• dispersal of seed and fruits

2. Plant depend on other plant for support
3. Animals depend on plants for

• Food
• Medicine
• Shelter
• Building materials
• Oxygen from photosynthesis

 

Food chain

A food chain is a sequence of organisms with arrows pointing from organisms being eaten to organism that eats it.

 

Example of food chainis

Its means that the Colobus monkey eats the mango and the lion eats the monkey. The arrow points to the eater, not what is being eaten.

 

A green plant is called a producer in the food chain because it produces food and is therefore the base of the food chain.

The other members of the food chain are called consumers since they either eat the producers (green plants) or they eat the animal that eats the producer.

 

Food webs

Is feeding relationship showing organisms feeding on more than one organisms.

 

 

 

Example of a food web