Question 1: Indicate
whether the following statements are True (T) or False (F).
(a) Unicellular organisms have one-celled body.
(b) Muscle cells are branched.
(c) The basic living unit of an organism is an organ.
(d) Amoeba has irregular shape.
Answer:
(a) Unicellular organisms have one-celled body.
(b) Muscle cells are branched.
(c) The basic living unit of an organism is an organ.
(d) Amoeba has irregular shape.
Question 2:Make a sketch
of the human nerve cell. What function do nerve cells perform?
Answer: The function of a nerve
cell is to transmit messages to the brain and also to take away messages from
the brain to the receptor organs. Thus, it controls the working of different
parts of the body.
Question
3:Write short notes on the following.
(a) Cytoplasm
(b) Nucleus of a cell
Answer:
(a) Cytoplasm: It is a fluid that fills the cell and occurs
between the plasma membrane and the nucleus. Cell organelles such as
mitochondria, ribosomes, Golgi bodies, etc. are suspended in the cytoplasm. The
cytoplasm helps in the exchange of materials between cell organelles.
(b) Nucleus of a cell: The nucleus is a spherical structure
generally present at the centre of a cell. The nucleus is composed of the
following components:
(i) Nuclear membrane: It is a double-layered membrane which
separates the contents of the nucleus from the cytoplasm. The nuclear membrane
has nuclear pores that allow the transfer of specific substances in and out of
the nucleus.
(ii) Nucleolus: It is a small spherical body that is not
bound by any membrane.
(iii) Chromosomes: These are thread-like structures that
carry genes. Genes contain information necessary for the transfer of
characteristics from the parents to the offspring. Thus, chromosomes play an
important role in the inheritance of characteristics.
Question 4:Which part of
the cell contains organelles?
Answer: Cytoplasm is the part of the cell that
contains various organelles such as mitochondria, ribosomes, Golgi bodies, etc.
Cytoplasm is a fluid that fills the cell and occurs between the plasma membrane
and the nucleus.
Question 5: Make
sketches of animal and plant cells. State three differences between them.
Answer:
Question 6: State
the difference between eukaryotes and prokaryotes.
Answer:
Prokaryotes
|
Eukaryotes
|
Nucleolus is absent.
|
Nucleolus is present.
|
Most prokaryotes are unicellular.
|
Most eukaryotes are multicellular.
|
Bacteria and blue-green algae are prokaryotic cells.
|
Fungi, plant, and animal cells are eukaryotic cells.
|
The nucleus is poorly defined due to the absence of a nuclear
membrane.
|
The nucleus is well defined and is surrounded by a nuclear membrane.
|
Cell organelles such as plastids, mitochondria, golgi bodies, etc.
are absent.
|
Cell organelles such as plastids, mitochondria, golgi bodies, etc. are
present.
|
.
Question 7:Where are
chromosomes found in a cell? State their function.
Answer: The nucleus contains
thread-like structures called chromosomes. Chromosomes play an important role
in the inheritance of characters. They carry genes that help in the transfer of
characters from the parents to the offspring.
Question 8: ‘Cells are
the basic structural units of living organisms’. Explain.
Answer: Cells constitute various
components of plants and animals. A cell is the smallest unit of life and is
capable of all living functions. Cells are the building blocks of life. This is
the reason why cells are referred to as ‘the basic structural and functional
units of life’. All cells vary in their shapes, sizes, and activities they
perform. In fact, the shape and size of the cell is related to the specific
function it performs.
Question 9:Explain why
chloroplasts are found only in plant cells?
Answer: Chloroplasts are found
only in plant cells. They contain a green pigment called chlorophyll. This
green pigment is important for photosynthesis in green plants. This chlorophyll
pigment traps solar energy and utilizes it to manufacture food for the plant.
Question 10:Complete the
crossword with the help of clues given below.
Across
1. This is necessary for photosynthesis.
3. Term for component present in the cytoplasm.
6. The living substance in the cell.
8. Units of inheritance present on the chromosomes.
Down
1. Green plastids.
2. Formed by collection of tissues.
4. It separates the contents of the cell from the
surrounding medium.
5. Empty structure in the cytoplasm.
7. A group of cells.
Answer:
Across
1. CHLOROPHYLL 3. ORGANELLE 6. PROTOPLASM 8. GENES
Down
1. CHLOROPLASTS 2. ORGAN 4. MEMBRANE 5. VACUOLE 7. TISSUE
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