Class 7 Science Lesson 3

1. Tick (✔) the correct alternative given below

a. Which phylum does a snail belong to?
✔ iv. Mollusca

b. Animals of which phylum are found only in the ocean?
✔ ii. Echinodermata

c. Which one is a unicellular animal?
✔ i. Paramecium

d. Which of the following is a characteristic of a cylindrical and unsegmented body?
✔ ii. Body is covered with cuticle

e. Which of the following is a unisexual parasite having a cylindrical and unsegmented body?
✔ ii. Ascaris

f. Which of the following is the main characteristic of the phylum of prawn?
✔ ii. Segmented body

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2. Fill in the blanks using suitable words given below: Tentacles, Bisexual, Annelida, Porifera, Protozoa

a. The animals having cylindrical and segmented body are kept in the phylum Annelida.

b. Flat animals are Platyhelminthes.

c. Sponges are kept in phylum Porifera.

d. All the single-celled animals are grouped in Protozoa.

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3. Answer the following questions

a. Write the name of the phylum of the following animals:

• Leech: Annelida

• Prawn: Arthropoda

• Starfish: Echinodermata

• Earthworm: Annelida

• Euglena: Protozoa

b. Why is a butterfly grouped in phylum Arthropoda?
A butterfly is grouped in phylum Arthropoda because it has jointed legs and a segmented body, which are the key characteristics of arthropods.

c. Write any three characteristics of phylum Protozoa:

1. Organisms are unicellular (single-celled).

2. They lack tissues and complex organ systems.

3. They mostly reproduce asexually by binary fission.

d. Why are sponges grouped in phylum Porifera?
Sponges are grouped in phylum Porifera because they are simple aquatic animals with numerous pores on their body surface, used for the passage of water and nutrients.

e. Name any two phyla in which bisexual animals are found:

• Platyhelminthes (flatworms)

• Annelida (segmented worms)

f. Write one similarity and one difference between flatworms and cylindrical worms:
Similarity: Both are invertebrates and have bilateral symmetry.
Difference: Flatworms have a flat body, whereas cylindrical worms have a round, elongated body.

g. Write any three characteristics of animals belonging to phylum Mollusca:

1. They have a soft and unsegmented body.

2. Most of them possess a hard external shell.

3. They have a muscular foot used for movement.

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h. Differentiate between the following pairs:

i. Protozoa and Porifera

ii. Arthropoda and Mollusca

iii. Earthworm and Pinworm

iv. Ascaris and Leech

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i. Sketch Neat Diagrams of the Following (Draw in notebook with labeling):

1. Amoeba – Show irregular shape, pseudopodia, nucleus, and vacuoles.

2. Earthworm – Show long segmented body with clitellum.

3. Snail – Show spiral shell, tentacles with eyes, and a muscular foot.

4. Hydra – Show tubular body with tentacles around the mouth area.

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j. Why are Ascaris and Earthworm classified into different phyla?

Even though Ascaris and Earthworm look similar externally, they belong to different phyla due to major internal differences:

1. Segmentation: Earthworm has a segmented body, Ascaris does not.

2. Coelom: Earthworm has a true coelom; Ascaris has a pseudocoelom.

3. Reproduction: Earthworms are hermaphrodites; Ascaris has separate sexes.

4. Mode of Life: Earthworms are free-living; Ascaris is parasitic.

5. Nervous System: Earthworms have a more developed nervous system than Ascaris.

These structural and functional differences justify their classification into phyla Annelida and Nematoda respectively.

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4. Answer the following questions:

a. Define cell.
The cell is the smallest structural and functional unit of life that can carry out all life processes independently. All living organisms are made of cells.

b. Why are cells considered the basic unit of life?
Cells are considered the basic unit of life because:

1. All organisms are composed of cells.

2. They carry out all life activities such as respiration, digestion, and reproduction.

3. Cells grow, divide, and pass on genetic information, making life possible.

c. Which component of a cell is called the powerhouse of the cell?
Mitochondria are called the powerhouse of the cell because they produce energy in the form of ATP (adenosine triphosphate) through the process of cellular respiration.

d. Sketch neat diagrams of animal and plant cells and label their parts:

• Plant Cell: Should show cell wall, cell membrane, nucleus, cytoplasm, large central vacuole, chloroplasts, mitochondria.

• Animal Cell: Should show cell membrane, nucleus, cytoplasm, mitochondria, small vacuoles, lysosomes.

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5. Mention the components found in an animal cell:

The major components of an animal cell are:

1. Cell membrane – Protective outer layer

2. Cytoplasm – Gel-like substance inside the cell

3. Nucleus – Control center of the cell

4. Mitochondria – Produces energy

5. Ribosomes – Protein synthesis

6. Endoplasmic reticulum (ER) – Transport of materials

7. Golgi apparatus – Packaging and transport

8. Lysosomes – Contain digestive enzymes

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6. Write any four components found in cytoplasm:

1. Ribosomes

2. Endoplasmic reticulum (smooth and rough)

3. Mitochondria

4. Golgi apparatus

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7. Why is the plant cell selected for studying cell structure?

Plant cells are often selected for microscopic study because:

1. They have clearly visible structures like a cell wall and chloroplasts.

2. Their large vacuole and rigid shape make them easier to observe under a microscope.

3. They are typically larger and have a more defined structure compared to animal cells.