Cell: The Unit of Life

1. Simple microscope
2. Concave mirror

1. 2000 times
2. 200,000 times

1. Bacteria, Amoeba
2. Nerve cells
3. White blood cells
4. Amoeboid

Nutrients, metabolic wastes, respiratory gases.

1. Cytoplasm
2. Nucleoplasm
3. Cell Wall

1. Difference between an organ and an organelle:

2. A plant cell has plastids while an animal cell does not have plastids.

1. Golgi complexes and Dictyosomes
2. Chloroplasts
3. Ribosomes
4. Lysosomes
5. Mitochondria

1. Cell wall
2. Endoplasmic Reticulum
3. Vacuoles
4. Chromosomes

1. False
   Corrected Statement— Prokaryotic cells have smaller ribosomes.
2. True
3. False
   Corrected Statement— Amoeba is an example of Eukaryotes.
4. False
   Corrected Statement— Nuclear membrane is absent in bacteria.

The Nucleus is the key to the life of the cell.

The cells behave like an organism. They carry out all the processes like an organism viz. respiration and elimination of wastes. They also have a life span like an organism. They grow, age, deteriorate and finally die. The dying cells are dissolved or destroyed by their own lysosomes. For example, Red blood cells of our body die after 120 days. These cells are continuously replaced by new cells in our body

Yes, an individual cell also excretes like an organism. Most of the waste substances are digested by the Lysosomes. Some cells may also release the waste product out through their cell membrane.

Yes, a cell also needs food for carrying out different processes. The food in the form of Glucose is broken down during respiration inside the mitochondria to release energy (ATP).

Ribosomes — Synthesis of proteins

Reason — The function of the ribosomes is synthesis of proteins.
Mitochondria are the powerhouse of the cell. It produces energy. Plasma membrane is selectively permeable, not freely permeable. Centrosome helps in cell division.

a single cell

Reason — A cell is smallest living entity. Therefore, all life starts as a single cell.
An egg is a reproductive cell, mainly in animals but not all organisms start life as an egg. A gene is a unit of heredity made of DNA and is not a complete living unit. Genes are parts of a cell. A chromosome is a structure made of DNA and proteins. It is a component of a cell.

cell membrane

Reason — Cell membrane is found in both animal and plant cell. The plant cell also has a cell wall, additional to cell membrane.
Chloroplasts is present only in plant cells. Centrioles is present mainly in animal cells. Cell wall is present only in plant cells. Cell membrane is present in both plant and animal cells.

Absence of centrosome

Reason — Centrosomes are only found in animal cells.
Both plant and animal cells have a cell membrane. Vacuoles are present in both plant and animal cells.

Cellulose

Reason — The cell wall of plant cell is made up of cellulose (a non living substance), a complex carbohydrate.
Proteins are important for structure and enzymes in cells but plant cell wall is not made of protein. Fructose is a simple sugar, not used to build the cell wall. Fatty acids are components of lipids. They are found in cell membranes, not cell walls.

Mitochondria

Reason — Mitochondria is the organelle responsible for breaking of glucose molecule to release energy. It is the site of cellular respiration.
Lysosome contains digestive enzymes. It breaks down waste and old cell parts. Ribosome is site of protein synthesis. It helps in making proteins. Centrosome helps in cell division.

Golgi apparatus

Reason — Golgi apparatus contains certain hydrolytic enzymes which helps to break the outer membrane of ovum.
Dictyosome acts just like the Golgi apparatus in plant cell. Centrosome helps in cell division and formation of spindle fibers. Lysosome contains digestive enzymes. It helps in breaking down waste materials.

Nucleolus

Reason — Nucleolus helps in Ribosomal RNA formation after which protein synthesis is done by ribosomes.
Nuclear membrane protects the nucleus and separates it from cytoplasm. Nuclear pore allow movement of materials in and out of nucleus. Nucleoplasm contains chromatin and nucleolus.

Anthocyanin

Reason — Anthocyanin is not associated with plastids; instead they remain dissolved in the cell sap.
Xanthophyll is present in chromoplasts. Carotene is present in chromoplasts. Chlorophyll is found in chloroplasts.

Cisternae

Reason — Hollow tubular structure of Golgi Complexes are known as Cisternae.
Microtubules are part of the cytoskeleton of the cell. Cristae found in mitochondria. Vesicles are small membrane-bound sacs. They are formed from Golgi, ER, or cell membrane but not structural tubules of Golgi Complexes.

P — Compound microscope, Q — Simple microscope.

Reason — Compound microscope was invented by Robert Hooke and simple microscope was invented by Antony Van Leeuwenhoek.
Electron microscope was invented by Ernst Ruska.

Nucleus has a delicate, protective surrounding layer (a) Nuclear membrane which is filled with a relatively dense fluid (b) Nucleoplasm. There are certain thread-like structures suspended in the fluid called (c) Chromatin. These thin thread-like fine structures become thick and ribbon-like during the time of cell division. These prominent ribbon-like structures are called (d) Chromosomes. Nucleus contains a spherical, dense body inside it, called as (e) Nucleolus which participates in protein synthesis.

1. Mitochondria
2. Ribosomes
3. Chromosomes
4. Centrosome
5. Lysosomes
6. Plasma membrane/cell membrane

(a) False
Corrected statement — All plant cells contain a cell wall.

(b) False
Corrected statement — The cell wall is made of cellulose.

(c) True

(d) True

(e) False
Corrected statement — Cytoplasm is the part of the cell which surrounds the nucleus.

(f) True

(g) False
Corrected statement — Anthocyanin are the pigments of fruits, which are dissolved in cell-sap.

23 pairs of chromosome are found in human cells.

The chemical substance constituting the genes is DNA. It stands for de-oxy ribonucleic acid.

1. Lysosomes consists of membranous sacs and secretes 40 types of digestive enzymes.
2. Centriole is surrounded by microtubules, located near the nucleus.
3. Very thin flexible, living membrane which is differently permeable, is called Plasma membrane.
4. More than 1000 chromosomes are found in the nucleus of certain Insects.
5. Genes are heredity units.
6. Leucoplast is a plastid which stores starch.

1. DNA — Deoxyribonucleic acid
2. RNA — Ribonucleic acid
3. ATP — Adenosine triphosphate
4. SER — Smooth endoplasmic reticulum
5. RER — Rough endoplasmic reticulum

1. petals of sunflower — chromoplast
2. ripe tomato — anthocyanin
3. skin of green mango — chlorophyll
4. cells of potato — no pigment

1. The part of cell having a definite structure and a definite function is called Cell organelle.
2. Various non-living substances like nutrients or pigments present in the cell are called Cell inclusions.
3. The liquid found inside the cell in which various organelles are found, is called Cytosol.
4. The watery solution present in the vacuoles is called Cell sap.
5. The semi-liquid substance that fills most of the part of cell (except nucleus) within the cell membrane is called Cytoplasm.

1. Centrosome - near nucleus (only in animal cells)
2. Chromosome - in nucleus
3. Genes - on chromosomes
4. Mesosome - Plasma membrane of bacterial cells
5. Plasmid - Cytoplasm of bacterial cells

Three features found only in plant cells are:

1. Presence of cell wall.
2. Presence of large vacuole.
3. Presence of plastids.

One feature only found in animal cell is presence of centrosome.

Cells are generally so little so that they can maximize their ratio of area to volume. They have to be ready to get the nutrients in and therefore the waste out quickly.The important point is that the area to the volume ratio gets smaller as the cell gets larger. Thus, if the cell grows beyond a particular limit, not enough material is going to be ready to cross the membrane fast enough to accommodate the increased cellular volume. That's why cells are so small.

The protoplasm cannot be analysed chemically because it has complex organic and living cell organelles which can disintegrate if chemicals are added to analyse. Also due to complexity of physical and chemical properties the ultimate chemical nature of protoplasm cannot be determined.

Cell is the basic unit of life. Cells aggregates to form tissue, organ, organ system and ultimately organism. Elephant has more cells compared to rat. The cell size is independent of the size of the entity. The cell size of a rat and that of an elephant are the same. Within the entity, the cell size is the same, it does not differ. However, what varies is the number of cells. Number of cells in a large entity such as elephant is much more compared to a smaller entity such as a rat.

The Cell Theory states three major points -

1. The cell is the smallest unit of structure of all living thing
2. The cell is the unit of function of all living things
3. All cells arise from pre-existing cells.

The theory was propounded in 1839 by Schwann and Schleiden. Rudolf Virchow in 1858 made an addition to the cell theory by saying that all cells arise from pre-existing cells.

The major functions are as follows-

1. Plasma membrane —

   1. Separates contents of cell from its surroundings.
   2. Regulates the entry of certain solutes and ions.
   3. Maintains shape of the cell in animal cells.

2. Ribosome —

   1. Protein synthesis

3. Lysosome —

   1. Intracellular digestion.
   2. Destroy foreign substances.
   3. They are referred to as 'suicidal bags' as they destroy cell organelles when they turn old or are damaged.
   4. Digest cartilages during formation of bones.

4. Mitochondria —

   1. Controls the cell functions.
   2. Referred to as ‘power house of the cell’, as energy is stored in the form of ATP.
   3. Involved in cellular respiration to release energy.
   4. Bearers of genes.

5. Golgi apparatus(in animal cells) —

   1. Synthesis and secretion of enzymes, hormones,etc.
   2. Acrosomes of sperms are formed.

6. Cytoplasm —

   1. Contains organelles perform multitude of functions.
   2. Performs all metabolic activities.

7. Asters of centrosome —

   1. Cell division – regulation and initiation.
   2. Spindle fibre formation.

8. Chromosomes —

   1. Passes genetic characteristics from parents to offspring.

9. Glycogen granule —

   1. Food for cells.

10. Vacuoles —

    1. Stores food, water, pigments and waste products.
    2. Renders turgidity to the plant cell.

Following are the differences between a living cell and a brick in a wall-

Given below are the following six features found both in plant and animal cells

1. Cell membrane is present.
2. Golgi body is present.
3. Liquid matrix known as cytoplasm is observed in the cell.
4. Mitochondria generates energy, is found in the cells.
5. Ribosomes are found. They are responsible for protein synthesis.
6. A prominent nucleus is observed.

(a) Figure B is a plant cell because in Figure B, the cell has a cell wall, a large vacuole and the vacuole is seen pushing the nucleus to the periphery.

(b) Cell structures common to both the types in the figure are:

1. Nucleus
2. Mitochondria
3. Ribosome
4. Cell membrane
5. Lysosome
6. Endoplasmic reticulum
7. Golgi body

(c) The structures found only in plant cells are Cell wall and Plastid. The structures found only in animal cells are Centrosome.

(a) Centrosome

(b) Centriole

(c) It helps in cell division by forming the spindle fibers that separate chromosomes during mitosis and meiosis.

(a) Bacteria

(b) Prokaryotic cell

(c) Ribosomes

(d) B labelled as cell membrane, is selectively permeable whereas C labelled as cell wall, is freely permeable.

(e) The structure (D) is a flagellum. It helps in locomotion of the bacterium.

A is False and R is True.

Reason — A is False because ribosomes are not the delivery system, they are the site of protein synthesis in the cell.
R is True as Golgi apparatus are the delivery system which is concerned with the secretions of the cell including enzymes, hormones, etc.

Therefore, A is False and R is True is the correct option.

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

Reason — A is true as leukoplasts are colourless plastids because they lack pigments.
R is true as leukoplasts are found in the non-photosynthetic parts of a plant. These parts do not perform photosynthesis. Therefore, leukoplasts in these parts lack pigments, making them colourless.

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

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

Reason — A is True because cristae are inward foldings or finger-like projections of the inner membrane of mitochondria.
R is True as these folds increase the surface area of the inner membrane. This provides more space for the enzymes and components needed for ATP production during respiration.
Since the reason correctly explains the function and importance of cristae, R is the correct explanation of A.

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

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

Reason — A is true as Euglena is a made up of a single cell, eukaryotic organism.
R is true because it has a well-defined nucleus and membrane-bound organelles.

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

A is True and R is False.

Reason — A is True because chromosomes carry hereditary information in the form of genes, which are passed from parents to offspring.
R is False as chromosomes are located in the nucleus, not suspended in the cytoplasm. They are made up of DNA and proteins not RNA.

Therefore, A is True and R is False is the correct option.

(a) Centrosome

(b) Golgi apparatus

(c) Lipoproteins

(d) Glycogen granules & fat droplets

(e) Cell wall