Class 8 Science
Question 1: Indicate whether the following statements are True (T) or False (F).
- Unicellular organisms have one-celled body. (T/F)
- Muscle cells are branched. (T/F)
- The basic living unit of an organism is an organ. (T/F)
- Amoeba has irregular shape. (T/F)
Answer: (a) True, (b) True, (c) False, (d) True
Question 2: Make a sketch of the human nerve cell. What function do nerve cells perform?
Answer: Nerve cells carry signals between organs and brain.
Question 3: Write short notes on the following:
Answer: A jelly-like substance is present between the cell and nucleus. It is called cytoplasm. Different cell organelles are present in the cytoplasm. Examples of cell organelles are; mitochondria, Golgi body, ribosomes, lysosomes, chloroplast, etc.
- Nucleus of a cell
Answer: This is a spherical structure which is present inside the cell; usually at the centre of the cell. Nucleus is surrounded by a double membrane called nuclear membrane. A dot-like structure; called nucleolus is present inside the nucleus. Nucleus contains chromosomes which are thread-like structures. Genes are present on chromosome. They are responsible for transferring characters from parents to their offspring.
Question 4: Which part of the cell contains organelles?
Question 5: Make sketches of animal and plant cells. State three differences between them.
|Difference Between Plant Cell and Animal Cell|
|Plant Cell||Animal Cell|
|Cell wall is present.||Cell wall is absent.|
|Chloroplast is present.||Chloroplast is absent.|
|Vacuoles are large.||Vacuoles are much smaller or absent.|
Question 6: State the difference between eukaryotes and prokaryotes.
|Nucleus is absent.||Nucleus is present.|
|All are unicellular.||Can be unicellular and multicellular.|
|Examples: Bacteria and blue-green algae||Examples: man, lion, horse, etc.|
Question 7: Where are chromosomes found in a cell? State their function.
Answer: Chromosomes are found inside the nucleus. Chromosomes are responsible for inheritance of characters from one generation to the next generation.
Question 8: ‘Cells are the basic structural units of living organisms’. Explain.
Answer: All organisms are made up of cells. The way a building is made up of bricks, an organism is made up of cells. Many cells group together to make a tissue, many tissues come together to make an organ, many organs come together to make an organ system and many organ systems make an organism. Thus, it is clear that cells are the basic structural units of living organisms.
Question 9: Explain why chloroplasts are found only in plant cells?
Answer: Chloroplast contains a green pigment called chlorophyll. Photosynthesis takes place in chloroplast. We know that green plants are capable of photosynthesis but animals do not have this capability. Hence, chloroplasts are found only in plant cells.