Cell: The Unit of Life

Correct Answer: C

1. The nucleus is an important cell organelle.
2. It controls cell activities.
3. It contains genetic material (DNA).
4. The nucleus was first observed in plant cells.
5. It was described by Robert Brown.
6. This discovery was made in 1831.
7. It was an important step in cell biology.
8. Later studies explained its functions.
9. Nucleus is present in eukaryotic cells.
10. Thus, Robert Brown described the nucleus in 1831.

Correct Answer: B

1. The nucleus contains different materials.
2. Some materials can be stained using dyes.
3. Basic dyes are used to stain nuclear material.
4. This stained material appears as a network.
5. It was studied by scientists.
6. Flemming identified this material.
7. He named it chromatin.
8. Chromatin contains DNA and proteins.
9. It forms chromosomes during cell division.
10. Thus, basic dyes stain nuclear material called chromatin named by Flemming.

Correct Answer: B

1. Interphase nucleus is the nucleus when the cell is not dividing.
2. It contains extended nucleoprotein fibres.
3. These fibres are called chromatin.
4. Another supporting network is called nuclear matrix.
5. These structures help maintain nucleus organization.
6. The nucleus also contains spherical bodies.
7. These are called nucleoli (singular: nucleolus).
8. Nucleolus helps in ribosome formation.
9. All these are present in interphase nucleus.
10. Thus, chromatin, nuclear matrix and nucleoli are present.

Correct Answer: B

1. Electron microscopy helps in detailed cell study.
2. It revealed the structure of the nuclear envelope.
3. The nuclear envelope surrounds the nucleus.
4. It is made of two parallel membranes.
5. These membranes are closely arranged.
6. There is a space between them.
7. This space is called perinuclear space.
8. It ranges from 10 to 50 nm.
9. It separates nucleus from cytoplasm.
10. Thus, nuclear envelope has two membranes with perinuclear space.

Correct Answer: B

1. The nuclear envelope has two membranes.
2. The outer membrane is the external layer.
3. It is continuous with the endoplasmic reticulum.
4. This connection helps in transport of materials.
5. The outer membrane has ribosomes attached.
6. These ribosomes help in protein synthesis.
7. This makes it similar to rough ER.
8. It plays an important role in cell function.
9. It links nucleus with cytoplasm.
10. Thus, outer membrane is connected to ER and bears ribosomes.

Correct Answer: B

1. The nuclear envelope surrounds the nucleus.
2. It has two membranes.
3. At certain places, these membranes fuse.
4. This fusion forms small openings.
5. These openings are called nuclear pores.
6. They are very minute in size.
7. They help in exchange of materials.
8. Substances move between nucleus and cytoplasm.
9. These pores are essential for cell function.
10. Thus, nuclear envelope has minute pores formed by membrane fusion.

Correct Answer: B

1. Nuclear pores are present in the nuclear envelope.
2. They act as gateways between nucleus and cytoplasm.
3. They allow movement of important molecules.
4. RNA molecules move out of the nucleus.
5. Proteins can move in and out.
6. This movement is in both directions.
7. It is essential for cell functioning.
8. It helps in gene expression and regulation.
9. Without pores, transport is not possible.
10. Thus, RNA and protein molecules pass through nuclear pores.

Correct Answer: B

1. The nucleus is an important cell organelle.
2. It controls cell activities.
3. Most cells contain only one nucleus.
4. This is the normal condition.
5. However, some cells show variation.
6. They may have more than one nucleus.
7. Such variations are commonly observed.
8. Example: muscle cells may be multinucleate.
9. Some cells may even lack a nucleus.
10. Thus, normally one nucleus is present but variations are frequent.

Correct Answer: B

1. Most cells have a nucleus.
2. However, some mature cells lose their nucleus.
3. This is an adaptation for specific functions.
4. Erythrocytes (RBCs) in many mammals lack nucleus.
5. This helps in efficient oxygen transport.
6. Sieve tube cells in vascular plants also lack nucleus.
7. This helps in transport of food materials.
8. These cells depend on neighboring cells.
9. Such specialization improves function.
10. Thus, erythrocytes and sieve tube cells lack nucleus.

Correct Answer: B

1. Some mature cells lack nucleus.
2. Example: erythrocytes and sieve tube cells.
3. Even without nucleus, they perform functions.
4. RBCs transport oxygen in the body.
5. Sieve tube cells transport food in plants.
6. They are metabolically active to some extent.
7. They are supported by other cells.
8. They are not dead like xylem cells.
9. Hence, they are considered living.
10. Thus, such cells are living despite lacking nucleus.

Correct Answer: B

1. The nucleus has an internal fluid called nucleoplasm.
2. It is also called nuclear matrix.
3. It contains important structures.
4. One of them is nucleolus.
5. Nucleolus helps in ribosome formation.
6. Another component is chromatin.
7. Chromatin contains DNA and proteins.
8. It helps in genetic functions.
9. Both are essential for nucleus activity.
10. Thus, nucleoplasm contains nucleolus and chromatin.

Correct Answer: B

1. The nucleolus is a structure inside the nucleus.
2. It is present in the nucleoplasm.
3. It plays a role in ribosome formation.
4. Nucleoli are clearly visible under microscope.
5. They have a distinct shape.
6. This shape is spherical.
7. There may be one or more nucleoli.
8. They are not membrane bound.
9. They are important for protein synthesis.
10. Thus, nucleoli are spherical structures.

Correct Answer: B

1. Nucleolus is present inside the nucleus.
2. It lies in the nucleoplasm.
3. It does not have a surrounding membrane.
4. Because of this, its contents are continuous.
5. There is no boundary separating it.
6. Hence, it mixes with nucleoplasm.
7. It is called non-membrane bound.
8. It helps in ribosome formation.
9. This is its key feature.
10. Thus, nucleolus is not a membrane bound structure.

Correct Answer: B

1. The nucleolus is present in the nucleus.
2. It is a non-membrane bound structure.
3. It plays an important role in ribosome formation.
4. Ribosomes require rRNA.
5. rRNA means ribosomal RNA.
6. The nucleolus actively synthesizes rRNA.
7. This is essential for protein synthesis.
8. Without rRNA, ribosomes cannot form.
9. Hence, nucleolus is very important.
10. Thus, it is a site for ribosomal RNA synthesis.

Correct Answer: C

1. Nucleolus is involved in ribosome formation.
2. Ribosomes are needed for protein synthesis.
3. Cells with high protein demand need more ribosomes.
4. Hence, nucleoli become larger.
5. They also increase in number.
6. This supports active protein production.
7. Such cells are metabolically active.
8. Example: gland cells.
9. Nucleolus activity reflects protein synthesis level.
10. Thus, larger nucleoli are seen in protein synthesizing cells.

Correct Answer: B

1. Interphase nucleus is seen when the cell is not dividing.
2. It contains chromatin material.
3. Chromatin appears as a loose network.
4. It is not clearly structured.
5. This network is made of nucleoprotein fibres.
6. These fibres contain DNA and proteins.
7. They later form chromosomes during division.
8. The structure is indistinct in interphase.
9. It helps in gene expression.
10. Thus, chromatin is made of nucleoprotein fibres.

Correct Answer: B

1. During interphase, nucleus is clearly visible.
2. It contains chromatin in loose form.
3. During cell division, chromatin condenses.
4. It becomes thick and visible.
5. These are called chromosomes.
6. The nucleus is not seen as a whole.
7. Instead, structured chromosomes appear.
8. This helps in proper distribution of DNA.
9. It is important for cell division.
10. Thus, structured chromosomes are seen during division.

Correct Answer: B

1. Chromatin is present in the nucleus.
2. It is made of nucleoprotein fibres.
3. It contains DNA as genetic material.
4. DNA is associated with proteins.
5. These basic proteins are called histones.
6. Some non-histone proteins are also present.
7. Chromatin also contains RNA.
8. These components help in gene regulation.
9. Chromatin forms chromosomes during division.
10. Thus, chromatin contains DNA, histones, non-histone proteins and RNA.

Correct Answer: B

1. Human cells contain genetic material in the form of DNA.
2. DNA is very long and thread-like.
3. In a single cell, it is about two metres long.
4. This DNA is packed inside the nucleus.
5. It is organized into chromosomes.
6. Humans have 46 chromosomes.
7. These are arranged in 23 pairs.
8. This packaging helps fit DNA inside the nucleus.
9. It also helps in proper functioning.
10. Thus, DNA is two metre long and present in 46 chromosomes.

Correct Answer: B

1. Chromosomes contain genetic material.
2. This genetic material is DNA.
3. DNA is packaged into chromosomes.
4. This packaging is complex.
5. It helps fit DNA inside the nucleus.
6. It also regulates gene expression.
7. Detailed study is done in higher classes.
8. Specifically in class XII biology.
9. It is an important topic in genetics.
10. Thus, DNA packaging is studied in chromosomes.

Correct Answer: B

1. Chromosomes are visible during cell division.
2. Each chromosome has a primary constriction.
3. This constriction is called centromere.
4. It holds the two chromatids together.
5. On both sides of centromere, special structures are present.
6. These are called kinetochores.
7. Kinetochores help in spindle fibre attachment.
8. They play a role in chromosome movement.
9. This ensures proper division.
10. Thus, centromere and kinetochores are important parts.

Correct Answer: B

1. Chromosomes are made of chromatids.
2. Each chromosome has two identical chromatids.
3. These are called sister chromatids.
4. They are joined at a specific point.
5. This point is called centromere.
6. Centromere holds the two chromatids together.
7. It plays a key role in cell division.
8. It helps in proper chromosome separation.
9. Without it, division cannot occur properly.
10. Thus, centromere holds two chromatids.

Correct Answer: C

1. Chromosomes have a centromere.
2. Its position varies in different chromosomes.
3. This variation is used for classification.
4. Based on centromere position, chromosomes are grouped.
5. There are four main types.
6. These include metacentric, submetacentric, acrocentric and telocentric.
7. Each type has a different shape.
8. This helps in identification.
9. It is important in genetics study.
10. Thus, chromosomes are classified into four types.

Correct Answer: D

1. Chromosomes are classified based on centromere position.
2. In metacentric chromosome, centromere is in the middle.
3. This divides the chromosome into two equal arms.
4. Both arms are of equal length.
5. It gives a symmetrical shape.
6. This type is easy to identify.
7. It is one of four types.
8. It is important in genetics study.
9. Shape depends on centromere position.
10. Thus, metacentric chromosome has equal arms.

Correct Answer: B

1. Chromosomes are classified based on centromere position.
2. In sub-metacentric chromosome, centromere is slightly off center.
3. It is not exactly in the middle.
4. This creates two unequal arms.
5. One arm is shorter.
6. The other arm is longer.
7. This gives an asymmetrical shape.
8. It is one of four chromosome types.
9. Helps in chromosome identification.
10. Thus, sub-metacentric chromosome has unequal arms.

Correct Answer: C

1. Chromosomes are classified based on centromere position.
2. In acrocentric chromosome, centromere is near one end.
3. This forms one very short arm.
4. The other arm is very long.
5. It gives an asymmetrical shape.
6. In telocentric chromosome, centromere is at the end.
7. So only one arm is visible.
8. These are different chromosome types.
9. Important for classification.
10. Thus, acrocentric and telocentric chromosomes differ by centromere position.

Correct Answer: C

1. Chromosomes may have secondary constrictions.
2. These regions do not stain easily.
3. They appear at specific locations.
4. Due to this, a small fragment is seen.
5. This fragment looks separated.
6. It is called a satellite.
7. Not all chromosomes have this feature.
8. It helps in identification.
9. It is a structural feature.
10. Thus, the fragment is called satellite.

Correct Answer: B

1. Cells contain different types of organelles.
2. Some are small vesicles.
3. These are membrane bound structures.
4. They are called microbodies.
5. Microbodies contain enzymes.
6. Enzymes help in metabolic reactions.
7. They are present in both plant and animal cells.
8. They perform important functions.
9. They help in detoxification and metabolism.
10. Thus, microbodies contain enzymes.