Cell — The Structure and Functions

Identify the part which contains pigment:

1. Cell membrane
2. Plastid
3. Centrosome
4. Cell wall

Answer

Plastid

Reason — Plastids contain pigments. Plastids are special cell organelles found in plant cells that contain pigments. Cell membrane, Centrosome, Cell wall does not contain pigments.

The organelle that controls all activities in a cell:

1. Nucleus
2. Vacuole
3. Plastid
4. Cytoplasm

Answer

Nucleus

Reason — Nucleus is the most important part of the cell. It regulates and coordinates various life processes of the cell. The nucleus is called the control center of the cell.
Vacuole stores water, food, and waste materials. Plastid contains pigments or stores food in plant cells. Cytoplasm is site of many chemical reactions, but not the control center.

A cell that is spherical in shape is:

1. White blood cell
2. Nerve cell
3. Red blood cell
4. Amoeba

Answer

Red blood cell

Reason — Red blood cells are spherical in shape and this specific shape enables them to hold more oxygen and easily flow through vessels and capillaries.
White blood cells typically have an irregular or amoeboid shape. Nerve cells are long, elongated, and highly branched. Amoeba is single-celled organism completely lacks a fixed shape.

The vacuole contains:

1. Water
2. Cell sap
3. Salts
4. Food

Answer

Cell sap

Reason — Vacuoles are filled with water and various substances in solution form called cell sap. The nucleus is called the control center of the cell.
Water is only one component of cell sap. Salts is dissolved in the cell sap. Food may be present in the cell sap but is not the complete contents.

The type of microscope that we use in our school laboratories is :

1. Simple microscope
2. Electron microscope
3. Compound microscope
4. Both (1) and (2)

Answer

Compound microscope

Reason — The type of microscope that we use in our school laboratories these days is the compound microscope. It is used to observe cells, tissues, microorganisms, and prepared slides.
Simple microscope has only one lens and not typically used for detailed observations in school biology labs. Electron microscope requires electricity and special preparation of specimens.

Which of the following lens is used in a simple microscope ?

1. A single biconcave lens
2. Two convex lenses
3. A single biconvex lens
4. Two concave lenses

Answer

A single biconvex lens

Reason — A Simple microscope consists of a single biconvex (convex) lens which produces a magnified image of an object. Two convex lenses are used in a compound microscope. A biconcave lens and two concave lenses diverge light rays and do not produce the magnified image required in a simple microscope.

Which of the following is not a unicellular organism ?

1. Bacterium
2. Paramecium
3. Spirogyra
4. Chlamydomonas

Answer

Spirogyra

Reason — Spirogyra is a multicellular green algae. Spirogyra is made up of many cells joined end-to-end, forming a long filament. Although Spirogyra looks like a thread, that thread is actually made up of many rectangular cells arranged in a row.
A unicellular organism is made up of only one cell. Bacterium is single-celled organism. Paramecium single-celled protozoan. Chlamydomonas single-celled green alga.

The outermost layer of the cell is known as :

1. Cytoplasm
2. Protoplasm
3. Epidermis
4. Plasma membrane

Answer

Plasma membrane

Reason — Each cell is surrounded by a cell membrane, also called plasma membrane. It is the outermost layer. The plasma membrane (or cell membrane) is the thin outer boundary of a cell. It surrounds the cytoplasm and controls the movement of substances into and out of the cell.
Cytoplasm is jelly-like material inside the cell. Protoplasm refers to the living contents of the cell. Epidermis is a tissue that forms the outer covering of plant or animal bodies.

The definite number of chromosomes in the cells of a human body is :

1. 23 pairs
2. 23
3. 46 pairs
4. 32

Answer

23 pairs

Reason — Every cell of the human body has 46 chromosomes which occur in 23 pairs. 23 chromosomes are inherited from the mother. 23 chromosomes are inherited from the father. Together they form 23 pairs (46 chromosomes).
23 is the number of chromosomes in a human gamete. 46 pairs would mean 92 chromosomes, which is incorrect. Humans do not have 32 chromosomes.

Which of the following are non-living cell inclusions ?

1. Nucleolus
2. Genes
3. Vacuoles
4. Chromosomes

Answer

Vacuoles

Reason — Vacuoles are the non-living inclusions in the cytoplasm bound by a membrane. These are filled with water and various substances in solution form called cell sap. Vacuoles are membrane-bound sacs that contain cell sap (water, salts, sugars, pigments, etc.) and are often considered non-living cell inclusions.
Nucleolus is living part of the nucleus involved in ribosome formation. Genes are functional units of heredity found on chromosomes. Chromosomes is living structures in the nucleus containing DNA and genes.

Assertion: Every organism, whether big or small, begins its life as a single cell.

Reason: The size of a single cell varies among different organisms.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true but R is not the correct explanation of A.

Reason — A is true as most organisms start life as a single cell (e.g., a zygote in animals and many plants). This cell then divides and develops into a multicellular organism.
R is true as the size of a single cell varies among different organisms, but this does not explain why every organism begins life as a single cell.

Therefore, Both A and R are true but R is not the correct explanation of A is the correct option.

Assertion: Root hairs are very important for the survival of plants as they absorb the raw materials for photosynthesis (water and dissolved minerals) from the soil.

Reason: Photosynthesis occurs in the chloroplasts of leaf cells.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true but R is not the correct explanation of A.

Reason — A is true as root hairs increase the surface area of roots and absorb water and minerals, which are essential raw materials needed for photosynthesis.
R is true as photosynthesis takes place in the chloroplasts, mainly present in leaf cells.

Therefore, Both A and R are true but R is not the correct explanation of A is the correct option.

Assertion: The cell membrane of a cell is selectively permeable as it allows the entry or exit of certain substances only.

Reason: The cell membrane acts as a rigid barrier, protecting cells from mechanical injury and pathogen attack.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is true but R is false.

Reason — A is true as the cell membrane (plasma membrane) is selectively permeable, meaning it controls what enters and leaves the cell (e.g., water, gases, ions, etc.).
R is false as the cell membrane is flexible, not rigid. The cell membrane does not act as a rigid protective barrier, protection is done by cell wall.

Therefore, A is true but R is false is the correct option.

Assertion: The nucleus is an integral part of a cell which contains a definite number of chromosomes in each cell of every species.

Reason: Chromosomes carry hereditary units called genes, responsible for transmitting characteristics from parents to offsprings.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Reason — A is true as the nucleus contains chromosomes, and each species has a characteristic number of chromosomes.
R is true as genes present on chromosomes control heredity and transfer traits from parents to offspring.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

Assertion: Leukoplasts are the kind of plastids which do not contain any pigment. They are colourless.

Reason: Leukoplasts do not play any significant role in plants due to the absence of pigments.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is true but R is false.

Reason — A is true as leukoplasts are colourless plastids because they lack pigments. They are commonly found in roots, seeds, and underground stems.
R is false as even though leukoplasts lack pigments, they perform important functions such as storage of starch, proteins, oils.

Therefore, A is true but R is false is the correct option.

Match the terms given in column A with those of column B :

Answer

Fill in the blanks with suitable words :

(i) Inside the nucleus, there is a small, spherical, darker body called ............... .
(ii) The plastids which do not contain any pigment are called ............... .
(iii) Cell wall is composed of ............... .
(iv) ............... contain yellow and red pigments.
(v) The process of preparing food by the plants is known as ............... .

Answer

(i) Nucleolus
(ii) Leukoplasts
(iii) Cellulose
(iv) Chromoplasts
(v) Photosynthesis

Identify the cellular structures with the help of the following clues :

(i) It is a colourless, translucent, viscous liquid found between the cell membrane and nuclear membrane.
(ii) It contains chromosomes.
(iii) It traps solar energy for the process of photosynthesis.
(iv) The selectively permeable, thin, delicate and flexible membrane.
(v) The hereditary unit which is located on the chromosomes.

Answer

(i) Cytoplasm
(ii) Nucleoplasm
(iii) Chloroplasts
(iv) Cell Membrane or Plasma Membrane
(v) Gene

Name the scientist who: (i) developed a simple microscope.
(ii) developed a compound microscope.

Answer

(i) Antonie Van Leeuwenhoek
(ii) Robert Hooke

Name the scientist who invented the first microscope.

Answer

The Scientist who invented the first microscope is Antonie Van Leeuwenhoek.

Who coined the term "cell"?

Answer

Robert Hooke coined the term "cell".

Briefly describe the three essential parts of a cell.

Answer

The three essentials parts of the cell are Cell membrane, Cytoplasm and Nucleus.

1. Cell membrane — Each cell is surrounded by a membrane which is called cell membrane. It is a living structure that is very thin, delicate and flexible. It has fine pores in it, through which only certain substances can pass in and out while others cannot. Therefore, the cell membrane is called selectively permeable.
2. Cytoplasm — The cytoplasm is a semi-liquid, colourless, and translucent substance. It is found between the nucleus and the cell membrane.
3. Nucleus — Nucleus is a small spherical mass mostly located towards the centre of the cytoplasm. It is the most important part of the cell. It regulates and coordinates various life processes of the cell. It plays an important role during cell division.

The cell membrane is called selectively permeable. Why?

Answer

The cell membrane is called selectively permeable because it allows only entry of specific substances, while holding back the others.

State the difference between Nucleus and Nucleolus.

Answer

Difference between Nucleus and Nucleolus:

State the difference between Cytoplasm and Protoplasm.

Answer

Difference between Cytoplasm and Protoplasm:

State the difference between Cell Wall and Cell Membrane.

Answer

Difference between Cell Wall and Cell Membrane:

List the major differences between a plant cell and an animal cell.

Answer

Difference between plant cell and animal cell:

Briefly discuss the importance of chromosomes in an organism.

Answer

The Nucleoplasm of the nucleus contains chromosomes. Chromosomes contain units called Genes. These genes are responsible for transmitting characteristics from parents to offsprings. Thus, the chromosomes are extremely important for an organism.

Fill up the blanks with the terms given below in the box:

pigments, wall, pre-existing , cell, vacuoles

(i) The ............... is the structural unit of all living things
(ii) All cells arise from ............... cells.
(iii) Animal cells have no cell ............... .
(iv) Plastids contain ............... .
(v) ............... are filled with water and dissolved substance.

Answer

(i) The cell is the structural unit of all living things.
(ii) All cells arise from pre-existing cells.
(iii) Animals cells have no cell wall.
(iv) Plastids contain pigments.
(v) Vacuoles are filled with water and dissolved substances.

Try to find the names of four cell organelles hidden in this maze. (Hint: The hidden words can appear horizontally or vertically; forward or backward or even mixed up). Write them in the lines provided. For example: "NUCLEUS" in the last row, seven backward letters.

Answer

The hidden four cell organelles are:
(i) Vacuole
(ii) Leucoplast
(iii) Chromoplast
(iv) Plastid

The solved maze is shown below:

Name the following

(i) Three essential parts of a living cell.
(ii) Three types of plastids.
(iii) Five parts of a nucleus.
(iv) Two cellular structures found only in plant cells.
(v) Two types of cellular membranes on the basis of their permeability.

Answer

(i) Cell Membrane, Cytoplasm, and Nucleus
(ii) Chloroplasts, Chromoplasts, and Leukoplasts
(iii) Nuclear membrane, Nucleoplasm, Nucleolus, Chromatin Network, Nuclear Pore
(iv) Cell Wall and Plastids
(v) Freely Permeable membrane (Cell Wall) and Selectively permeable membrane (Cell Membrane)

Write one important role of the following :
(i) Nerve cells
(ii) Genes
(iii) Leukoplasts
(iv) Muscle cells
(v) Nucleus

Answer

(i) Nerve cells conduct messages in the form of impulses between different parts of the body and the brain.
(ii) Genes are responsible for transmitting characteristics from parents to offsprings.
(iii) Leukoplasts store starch, fats and proteins in plant cells.
(iv) Muscle cells are responsible for movement of body parts. It is the ability of the muscle cells to contract and relax.
(v) Nucleus regulates and coordinates various life processes of the cell.

Define the terms given below :
(i) Cell
(ii) Cytology
(iii) Protoplasm
(iv) Cytoplasm
(v) Chloroplast

Answer

(i) Cell — A cell can be defined as the basic structural and functional unit of all living things.
(ii) Cytology — Cytology is the study of cells, encompassing their structure, function, and interactions with their environment.
(iii) Protoplasm — Protoplasm is the living substance of the cell. It is made up of the cytoplasm and nucleus.
(iv) Cytoplasm — The cytoplasm is a semi-liquid (viscous), colourless and translucent substance. It is found between the nucleus and the cell membrane.
(v) Chloroplast — Chloroplasts are green plastids, that trap the solar energy for photosynthesis.

Briefly describe the structure of nucleus and mention its any two function.

Answer

Nucleus is a small spherical mass mostly located towards the centre of the cytoplasm. Nucleus has the following parts:

1. A delicate, porous nuclear membrane which encloses a relatively dense Nucleoplasm.
2. Inside the nucleoplasm the small darker body Nucleolus is present. The nucleoplasm contains chromosomes.

Below diagram shows the structure of the Nucleus:

The two functions of nucleus are:

1. It regulates and coordinates various life processes of the cell.
2. It plays an important role in cell division.

Name the scientist who coined the term "cell". How many lenses did he use in his microscope? What did he observe under his microscope?

Answer

Robert Hooke is the scientist who coined the term "cell". He used two lenses in his microscope. Under his microscope, he examined a very thin slice of a dead cork (the bark of the trees) and observed a cluster of box-like cubicles piled up together.

Name the three essential parts of the cell. Briefly describe the structure of cell membrane.

Answer

The three essential parts of the cell are:

1. Cell membrane
2. Cytoplasm
3. Nucleus

Structure of Cell Membrane:

1. Each cell is surrounded by a cell membrane, also called plasma membrane.
2. It is very thin, delicate and flexible.
3. It is a living structure present in both animal and plant cells.
4. It has fine pores in it, through which only certain substances can pass in and out, while others cannot. Therefore, the cell membrane is called selectively permeable.

Write the significance of cell division (4 points).

Answer

Cell division is the necessity for the existence of all living organisms, including plants. This is because new cells need to be produced for-

1. Replacement
2. Repair
3. Reproduction
4. Growth

The diagram given alongside represents a certain kind of cells found in humans. Study the same and answer the following questions.

(i) Identify the kind of cells.
(ii) Label the guidelines 1 to 3.
(iii) Which of the above labelled part regulates and coordinates the various life processes of the cell ?
(iv) If we were to prepare a slide of the cells shown above, what stain will we use in order to clearly see the cells ?
(v) How many chromosomes are found in the part shown as 2 ?

Answer

(i) The given diagram shows human cheek cells.

(ii) The guidelines 1 to 3 are:
1 → Cytoplasm
2 → Nucleus
3 → Cell Membrane

(iii) 2 → Nucleus

(iv) Methylene blue stain.

(v) 23 pairs of chromosomes are found in the part 2, i.e., Nucleus.

The diagram given alongside represents a cell. Study the same and answer the following questions :

(i) Is it a plant cell or an animal cell ? Give reason in support of your answer.
(ii) Label the guidelines 1 to 8.
(iii) Name one structure shown in the figure which is found in both plant and animal cells, but with different sizes.
(iv) What is the protective membranous covering of the part shown as 4 called ?
(v) Name any two organelles.

Answer

(i) The given diagram shows an Animal cell. It does not have a cell wall and plastids. Also, the vacuoles are small, unlike the big ones present in a plant cell.

(ii) The guidelines 1 to 8 indicate:
1 → Cell Membrane
2 → Centrosome
3 → Cytoplasm
4 → Nucleus
5 → Nucleolus
6 → Chromosomes
7 → Mitochondria
8 → Vacuole

(iii) Vacuoles are present in both plant and animal cells. They are larger in size in plant cells, but smaller in size in animal cells.

(iv) Part 4 is Nucleus. Its protective membranous covering is called Nuclear membrane.

(v) Two organelles are — mitochondria and endoplasmic reticulum.

For a classroom activity, class 6 students collected pond water samples from near their school. The water looked dirty and greenish, yet they couldn't spot any organism with the naked eye. Their Biology teacher then helped them observe the samples they collected under a microscope. To their surprise, they saw tiny organisms that had no visible legs or hands but showed quick movements.
Answer the following questions :

(i) Identify the organisms based on the clues :

(a) Irregular-shaped, unicellular animal.

(b) A unicellular, slipper-shaped animal that moves with the help of cilia.

(c) A unicellular plant with flagella.

(ii) Mention one biological function that occurs in both unicellular and multicellular organisms.

(iii) Why do cells differ in their shapes?

Answer

(i) The organisms based on the clues :

(a) Irregular-shaped, unicellular animal is Amoeba.

(b) A unicellular, slipper-shaped animal moving with cilia is Paramecium.

(c) A unicellular plant with flagella is Chlamydomonas.

(ii) Respiration occurs in both types of organisms to release energy from food.

(iii) Cells differ in shape because cell shape is determined by the function of the cell.