Classification of Living Things Class 7 Biology

Selina Concise ICSE Solutions for Class 7 Biology Chapter 2 

Classification of Plants

Synopsis:

• Classification means grouping things together on the basis of certain common features.
• The classification helps us to identify the living organisms and to study them more easily and systematically.
• The plants can be classified as follows on the basis of their size and shape as:
  1. Herbs
  2. Shrubs
  3. Trees.
• The plants which have soft, green and perishable stems are called herbs.
  Example: maize, rice, mint etc.
•  The plants with woody stems, with branches of almost equal size arising from the stem immediately above the soil are called shrubs.
  Example: Lemon, jasmine etc.
• The plants which are tall and have hard, woody stems and bear woody branches, twigs and leaves at some distance above the ground are called trees.
  Example: Coconut and palm.
  Non – flowering plants are called Cryptogams
• Flowering plants are called Phanerogams.
• The non-flowering plants can be further classified as:
  1. Thallophyta (Bacteria, Fungi and Algae)
  2.  Bryophyta (Mosses)
  3. Pteridophyta (Ferns)
• Thallophyta do not bear-roots, stems or leaves.
• Mosses have stems and leaves but no roots rather have
  thread-like structures called rhizoids.
• Mosses are called Amphibians of the plant group as they need water to reproduce.
• Spores are not seeds.
• Spores are tiny structures capable of producing new plants.
• The flowering plants can be further classified into
  1. Gymno sperms.
  2.  Angiosperms.
• The flowering plants that bear seeds but no fruit are called Gymnosperms. Their seeds are thin and naked.
• The characteristic feature of gymnosperms is that their roots are well developed, trunk is thick and woody and their leaves are long and pointed.
•  The female part of the angiosperms plant is called ovary.
•  The plants can be classified on the basis of life span as:
  1. Annuals
  2. Biennials
  3. Perennials
•  The plants which live for only one season in a year are called annuals.
  Example: Wheat, rice, pea, sunflower.
•  The plants which complete their life cycle in two years, i.e. in the first year they bear the vegetative parts while in the second year they bear flowers, fruits and seeds are called
  biennials.
  Example: Carrot, potato, cabbage.
•  The plants which live for more than two years and bear flowers, fruit and seeds every year.
  [They may even live for hundreds of years] are called
  perennials.
  Example: Banyan, pine.
• The perennial plants can be further divided as
  1.  Deciduous: Shed their leaves once in a year usually before winter. •
     Example: Oak, mulberry.
  2. Evergreen: These never shed their leaves all at one time. They keep shedding their leaves throughout the year. Example: Mango, guava etc.
• The self – nourishing living beings are called autotrophs. Those nourishing on others are called heterotrophs.
•  On the basis of habitat, the plants can be classified as.
  1. mesophytes
  2. xerophytes
  3. hydrophytes.
•  Mesophytes : The plants which grow on land and need moderate amount of water for their survival.
  Example: Mango,apple.
• Xerophytes:
  
  1.  The plants which grow is deserts and need minimum amount of water for their survival.
  2.  These have thin and spiny leaves to minimise water loss.Example: Cactus, Babul etc.
• Hydrophytes:
  1. The plants need maximum amount of water and hence grow in water.
  2.  They have either very small or no roots at all.
     Example: Lotus, water lily etc.

Activity 1
Visit a garden park with your teacher or parents and take along with you, a notebook and a pencil. In the park, you would see a large variety of plants some very small, some with average height and some very tall. These plants differ in their features like shape, size (small/medium/tall) and life span. Observe these features carefully (you may even take help from the Gardner) and note down in the table given below.
Classify these plants in their respective appearance and categories:
Answer:

Activity 2
Visit a nearby garden or park. Observe the different types of plants small and large, growing there. If permitted by the care-taker collect samples of as many types of plants as you can by plucking. Be sure that you do not damage the plant and collect only one specimen of each type. Take them to your school and record them according to their categories in your notebook
Answer:
 

Activity 3

You will see two parts in gram seed. Each part of the seed in called cotyledon. In maize seed, you will see only one cotyledon. Can you tell which seed among them is monocotyledon and which is dicotyledon ?
Monocot : Dicot
Answer:
Monocot: maize seed Dicot: gram seed

Review Questions 

1.Tick (✓) the appropriate answer :

(i) The two main categories of plants recognised on the basis of whether they produce fruits or not:
a) Biennials and annuals
b) Angiosperms and gymnosperms
c) Herbs and shrubs
d) Bryophyta and pteridophyta

(ii) Unicellular organisms with a proper nucleus are known as :
(a) Protista
(b) Monera
(c) Fungi
(d) Algae

(iii) Amoeba belongs to :

(a) Monera
b) Protista
(c) Fungi
(d) Algae

Short Answer Questions

1. Name the categories of the following:

1.  Plants which do not have roots, stems, and leaves: Thallophyta.
2.  Plants with no roots, but have stems and leaves: Bryophyta  or Mosses.
3.  Plants with roots, stems, and leaves, and which bear spore- producing bodies: Pteridophyta or Ferns.
4.  The amphibians of the plant kingdom mosses (Bryophytes)

2. Give two characterists and one example of each of the following:

(i) Algae:
Ans. Example: Spirogyra
(a) these are found in stagnant water of ponds, growing as green scum
(b) they have chlorophyll

(ii) Fungi:
Ans. Example: Mushroom
(a) They cannot prepare their food
(b) Most fungi live on dead and decaying organic matter

(iii) Monocot:
Ans. Example: Maize
(a) They have seeds with one cotyledon
(b) Cotyledon usually becomes the embryonic first leaves of a seedling

(iv) Dicot
Ans. (a) They contain two cotyledons in their seed.
(b) They have network like (reticulate) venation in their leaves.
Examples : gram, rose, mango.

(v) Bryophyta
Ans. (a) They have stems and leaves but no roots.
(b) They are non-flowering plants.
Examples : mosses, liverworts.

(vi) Pteridophyta
Ans. (a) They are non-flowering plants i.e. do not produce flowers are seeds. They reproduce through spores
(b) They have feather like leaves divided into leaflets. Example : ferns

(vii) Thallophytes
Ans. (a) These plants do not have roots, stems or leaves.
(b) They are non-flowering plants.
Examples : Bacteria, fungi, algae

3. Differentiate between

(i) Algae and fungi

Algae

1.  Usually green having chlorophyll
2.  Found in stagnant water of ponds.
3.  Are usually Autotrophs e.g. Spirogyra

Fungi

1. Do not have chlorophyll
2. Found on dead and decaying organic matter.
3. Are usually saprophytes. e.g. Bread mould

(ii) Monocot and dicot plants.

Monocot
The plants which contain only one cotyledon in their seeds.
example: Grass, Maize

Dicot
The plants which contain two cotyledons in their seeds.
example: Brinjal, Mango

(iii) Autotrophs and heterotrophs

Autotrophs

1. They can make their own food using solar energy.
2.  These include green plants having chlorophyll.
3.  They are also called producers.

Heterotrophs

1. They cannot make their own food and depend on autotrophs or other heterotrophs for food.
2. These include animals and non-green plants.
3. They are called consumers.

(iv) bacteria and amoeba

Bacteria

1. Bacteria are one of the smallest and structurally the simplest organisms.
2.  Bacteria are unicellular cells
3.  They are found every-where air, water, soil, the bodies of humans, plants and animals.
4.  They are visible only under a high powered light microscope

Amoeba 

1.  Amoeba is one of the simplest animals.
2. It is made up of just one single cell.
3. Amoeba is found in ponds, ditches and other places with stagnating water.
4.  They can be seen under the microscope only

(v) mosses and ferns
mosses

1.  Mosses grow as green, velvety layers in moist places such as damp soil, on the bark of trees, and on damp walls.
2. These plants have stems and leaves, but no roots

ferns

1.  Ferns are grown in most of the gardens for their beautiful leaves.
2. They bear well-formed leaves, stems and roots.

(vi) Angiosperms and gymnosperms
Angiosperms

1. These plants bear seeds inside a fruit.
2.  Leaves are usually broad.
3. They usually shed their leaves every autumn.
4. Examples: rose, sunflower, sugarcane.

gymnosperms

1. These plants bear naked seeds called cones. Fruit is absent.
2.  Leaves are usually needle like. They usually remain green throughout the year.
   Examples: Pine, cedar, fir.

Long Answer Questions
(Write the answers in your note book)

Question 1.

What name is given to bacteria found in the root nodules of pea plants ? State their importance.
Answer:
Rhizobium bacteria are found living in the root nodules (small swollen structures on roots) of leguminous plants like the pea, bean etc. These bacteria trap the nitrogen from the atmosphere and convert it into nitrates (mineral salts) which can be easily absorbed by the plants from the soil along with the water. It is observed here that the bacteria provide food to the host plant and the host plant in turn provides shelter for the bacteria. This kind of relationship wherein two organisms live in harmony each benefiting from such a relationship is called symbiosis. The organisms are called symbionts.

Question 2.
Briefly explain four types of bacteria on basis of their shape.
Answer:
There are four common forms of bacteria – coccus, bacillus, spirillum and vibrio.

1. Coccus form: These bacteria are spherical or ovoid in shape.
2. Bacillus form (bacillus : rod) These are rod-shaped. These may also occur singly or in group of two’s or three’s, joined end to end in long chains.
3. Spirillum form: These are spiral-shaped.
4. Vibrio form: These are short, curved, appearing comma- shaped. Chloera bacteria (Vibrio cholerae) are of vibrio type.

 Question 3.
Give reasons for the following:
(i) Bryophytes are called amphibians of plant kingdom.
(ii) Amoeba does not have any regular shape.
Answer:

1. Since bryophytes grow on land but need water for reproduction (like frogs in animals), they are called the amphibians of plant kingdom.
2. The body of Amoeba is irregular in shape. The outer covering of the body is the cell membrane. A prominent nucleus lies in the center surrounded by cytoplasm.

Question 4.
What is a contractile vacoule ? State its function in amoeba.
Answer:
Excess of water from the body of the amoeba is collected in the contractile vacuole. Ammonia is soluble in water. Hence, sometimes ammonia is expelled out along with the water from the contractile vacuole.
Function: The contractile vacuole expands when there is water in it and shrinks when the water is released into the surrounding.

Question 5.
List out Jive uses each of bacteria and fungi in our lives.
Answer:
The uses of Bacteria are :

•  Lactobacilus bacteria is used for curdling of milk (formation of curd from milk). It converts the milk sugar (lactose) into lactic acid, giving the sour taste to the curd.
•  Certain bacteria like Acetobacter ferment fruit juices into vinegar (acetic acid).
• Tanning of leather: Certain bacteria are used in curing of animal hides and skin.
• Retting of fibres: Jute fibres are separated and made softer by the use of bacteria.
• Formation of compost and manure: Cow dung, horse dung and agricultural wastes are subjected to bacterial action which causes their decay and produce very useful manure.

The uses of Fungi are:

• Fungi are an important source of food. Some mushrooms such as Morechella and Agaricus are edible.
• Yeast, a unicellular fungus, is important in bakeries as it is used in the making of bread. It is also important in the breweries for making alcohol.
• Yeast also produces vitamin B.
• Fungi, like bacteria, are also good decomposes. They decompose dead organic matter and return the nutrients back into the soil.
• Penicillin an important antibiotic is obtained from a fungus called Penicillium notatum.