Getting To Know Plants
Category : 6th Class
Learning Objectives
1. Plants can be classified into herbs, shrubs and frees.
2. A flowering plant has 2 septum -shoot and root septum.
3. Roots are of two types-top and fibrous.
4. Stem conducts water and minerals. Some stems store food and water.
5. Leaf prepares food for the plant by photosynthesis.
6. Flower is the reproductive part of the plant.
7. Pollination and fertilization result in the formation of fruit.
Plants grow all around us. They grow on land as well as in water. There are about 2, 50, 000 types of plants. Carolusinneaus put forward a method of namingliving things and classifying them into groups.
Classification of Plants:
I. Plants were divided into two broad groups - flowering plants andnon-flowering plants. Flowering plants are rose, mango, sunflower and jasmine, etc. Ferns & mosses are non-flowering plants.
II. Based on their life span: Depending on the duration of their life cycle, there are three types of plants:
(i) Annuals: The life cycle of these plants is completed in one yearThey grow, produce flowers and seeds during this period and thendie. E.g. wheat, pulses, gram.
(ii) Biennials: These plants complete their life cycle in two years. These plants are usually herbs.
(iii) Perennials: These remain alive for many years. These are mostlyshrubs and trees. They keep producing flowers, fruits and seeds year after year. E.g. neem, mango. Hibiscus, etc.
III. Classification based on the size and nature of stem. Based on nature of stem plants can be grouped into
(a) Herbs
(b) Shrubs
(c) Trees
(d) Climbers
Parameters |
Herbs |
Shrubs |
Trees |
Climbers |
Creepers |
Size |
Very small, less than 1 m high |
medium size 1-3 m high |
tall more than 3 m high |
can be very tall |
can be very long |
Nature of stem |
green, tender stem, few brances |
hard, but not very thick branches near the base of stem |
hard, woody thick stem, branches on upper part of stem |
soft stem, needs support to stand |
soft stem that cannot stand erect, creep on soil surface |
Example |
tomato, mint |
lemon, rose, Hibiscus |
neem, mango, peepal |
grapevine, gourd, pea, money plant |
strawberry, mint, Oxalis |
Plant Systems
Various parts of a plant perform different functions to keep it alive.
Parts of a plant
(i) It helps in holding the plant firmly in the soil.
(ii) They absorb water and dissolved minerals from the soil.
(iii) Some roots, like carrot and radish, store food for the plant.
Plants need water and minerals to stay alive-suck these from the soil and send them up to the rest of the plant. Roots generally grow in the direction where they find the correct amount of air, water and minerals needed forthe plant.
Root Systems
Tap roots
A typical root consists of the following parts:-
(a) Primary root
(b) Secondary root
(c) Root cap and root hair (temporary)
Tap roots are true roots. They generally grow vertically downwards and giveoff lateral branches from main root. They develop from radical of embryo (germinating seed).
Secondary root: These are lateral branches of the primary root which holdon to the soil and give mechanical support to the plant.
Root cap: It covers the tip of the main root. It protects the growing root tip.
Plants with top roots bear leaves that are generally broad and have a crisscross network
Fibrous root of grass: The fibrous roots generally grow in clusters ofslender roots from the base of stem. These do not develop from radical of embryo. They develop from any other part of plant. They do not haveany secondary or primary root system. These do not have root caps.
Plant with fibrous root bear leaves which are long and tapering and have parallel venation.
E.g. - wheat, rice, corn, grass and barley etc.
Modifications of Roots:
1. Storage: Roots of carrot, radish, sweet potato and beet root store food prepared by plant. Let eat these roots. Plants use this food when conditions are unfavorable.
Do You Know
The high energy roots of baobab tree are much sought after when nothing else grows during famine. In Rajasthan roots of khejri trees are eaten when crops fail.
2. Aerial roots: The banyan tree has roots that grow down from its branches.
They, provide support to the spreading branches of the huge tree. Suchroots are called prop roots.
Do You Know
The big banyan tree in the Indian Botanical Garden near Kolkatta have more than 900 prop roots.
3. The roots in sugar cane and maize provide extra support to the thinstem. These are called stilt roots.
Do You Know
Pneumatophores are breathing roots seen in mangroves and other plants growing in swampy environment. They grow vertically upward, against gravity and help the plant get oxygen.
The Shoot System
The aerial part of the plant is called the shoot system. It consists of two regions.
The stem: It forms the main axis on which leaves, buds, flowers, branches and fruits arise.
Stem develops from plum ale of the embryo of the seed. Unlike roots, thestem has distinct regions called nodes from which the leaf arises. Regionbetween two successive nodes is called internode. Angle between the stemand leaf is known as axil. Axil has a bud called axillary bud. Bud grow into abranch or a flower. At the tip of the stem is the terminal bud which is responsiblefor elongation of the plant.
Main differences between Root and stems |
||
|
Root |
Stem |
1 |
It is descending non green part of the plant grows towards the soil and water and away from sunlight. |
It is ascending portion of axis of plant. It grows away from soil and water but towards sunlight. |
2 |
It is not differentiated into nodes and intendeds. |
It is differentiated into nodes and intemodes. |
3 |
Root has rootlets and root hair and does not bear leaves, buds and flowers. |
Stem bears leaves, buds and flowers. |
Functions of stems
1. It holds leaves in position and keep the plant upright.
2. It bears flowers, fruits, buds, leaves, etc., leaves are arranged in such away that they are exposed to sunlight.
3. Green stem has chlorophyll and can carry out food manufacturing byphotosynthesis.
4. It conducts water and minerals from roots to leaves. It also carries foodmade by leaves to other parts of the plant. Xylem tissue carries water and minerals and phloem tissue carries prepared food.
Stem Modifications
1. Storage of water: Stems of plants like cactus swell up to store water inthem. They also have a waxy layer for protection from the sun.
2. To manufacture food: Stems of cactus become leaf like and flattened to perform photosynthesis.
3. For protection: Stems may be modified as thorns (as in Bougamvillea), prickles (as in rose), to protect the plant from being eaten by animals.
4. For support: Stems of some climbers like grapes are modified to form special structures called tendrils. These help the climber plant to coil round the support.
Do You Know
Cacti can gather and hold a lot of water in their stems. The water is not pure and clear but is thick viscous liquid. It is drinkable and has been known to save many lives in the desert.
5. For storage of food: Potato, onion and ginger are modified stems that store food. There are three kinds of underground stems: Bulbs of onions & garlic, tuber of potato and rhizome of ginger.
Modification of root for storage of food
6. For multiplication of the plant: Rhizomes, bulbs and tubers also help in multiplication of plant. Some plants like rose multiply by stem cutting. The leaf:
The leaf is a flat, green lateral outgrowth of the stem, arising from the node.
The flat portion of the leaf is called leaf blade or lamina. The lamina is attached to the stem by a stalk called petiole. Such leaves are called petiolate leaves and if the petiole is not distinct, the leaf is called sessile. At the tip of the leaf, lateral outgrowths called stipules are present. Petiole continues into parts of a leaf the leaf as midrib. Midrib branches out into venation of veins which may be criss cross in reticulate venation and parallel to each other in parallel venation. Midrib supports the leaf and the veins distribute water and nutrients throughout the leaf. Reticulate venation is seen in plants with tap roots and parallel venation is seen in plants with fibrous roots.
The green colour of the leaves is due to presence of a pigment calledchlorophyll. They may sometimes have yellow, red or violet spots besides green colour. Such leaves are called variegated leaves.
Leaf surface also has small pores or openings called stomata which allow exchange of gases for photosynthesis, transpiration and respiration.
Functions of the Leaf
1. Photosynthesis: Leaves make food in the presence of sunlight with thehelp of water from soil and carbon dioxide from air. Chlorophyll trapssunlight and provides energy to the plant for making food by the leavesis called photosynthesis.
The sugar that is prepared by leaves in glucose. This change to starchand is stored in plant fruits, roots and stems.
Test for starch: When iodine/solution is added to a leaf which hasbeen boiled in water and spirit, show blue-black colouration. This confirms presence of starch.
Experiments:
Through these holes, oxygen enters the leaves and carbon dioxide isreleased.
Modifications of leaf
They trap the insects and digest them to derive proteins.
E.g. Nepenthes and Venus fly trap.
Arrangement of leaves on the stem is called phyllotaxy. There are three types of phyllotaxy such as, alternate, opposite and whorled.
Flower
The most attractive part of a plant is its flower. Many flowers have sweet smelland some have emplacement smell. Flower is the main reproductive organ off lowering plant.
Parts of a flower
Pedicel: It is the axis in bearing the flower and joins it to the stem.
Thalamus: The upper part of pedicel is wide and slightly swollen. It is called receptacle or thalamus.
In an angiosperm flower, four whorls of leaf like structures arise from the thalamus. These are called floral leaves.
Ovary contains small swells which contains the female gametes.
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Fertilization
Keywords
Concept Map
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