Cell Structure And Functions

Microscope was essential for the study of cells.

The basic similarity among all the living organisms is that they all are made up of cells.

Robert Hooke in 1665 observed a thin slice of cork through a microscope and coined the term ‘cell’

Plasma membrane is the outermost layer of an animal cell.

Cell organelles are present in the cytoplasm.

Mitochondria and Endoplasmic reticulum.

Mitochondria is the site of respiration.

Gene is a unit of inheritance in living organisms.

Nucleus is the largest floating body generally in the center of a cell.

Nucleus controls all activities of the cell, hence it is also called Master or Director of the cell.

They possess photosynthetic pigment called chlorophyll.

Plant cells are surrounded by a cell wall.

Animal cells do not have a cell wall around them.

Cell wall

Plant cells differ from animal cells in having an additional layer around the cell membrane termed cell wall.

Chloroplast is the organelle of a plant cell where photosynthesis takes place.

Cell wall protects outside to the plant cell.

Mitochondria releases energy from food in the plant cell.

Coloured plastid (Chromoplasts) gives the red colour in tomatoes.

A plant cell has a large vacuole.

Cell wall and plastids are present only in a plant cell.

Nerve cell transmit message between the brain and other parts of the body.

Muscle cells in the human body can contract and relax.

The spindle-shaped cells present in the human body are muscle cells.

A muscle cell is pointed at both ends and has a spindle shape.

White blood cells present in human blood is a single cell (other than Ameoba cell) which can change its shape.

Amoeba is a single cell which behaves like a complete organism.

The bird’s egg are very large cell which can be seen easily with naked eye while bacterial cells are extremely small which can be seen only through a microscope.

(a) True, unicellular organisms (single celled organisms) are made up of only one cell.

(b) False, muscle cell are not branched.

(c) True, Amoeba have changing shape.

(d) False, All the cells in our body exhibit variety of shapes and sizes so that they can perform different functions.

(e) False, A hen’s egg is not a group of cells. It is a single cell.

(f) False, the basic living unit of an organism is cell.

Cell is the smallest unit of life.

Cell is structural and functional unit of all living beings.

The basic parts of all the cells are- cell membrane, cytoplasm and nucleus.

The parts which are present only in plant cells are- Cell wall, chloroplasts and large vacuole.

Plasma membrane controls the flow of substance in and out of a cell.

Nucleus controls all the activities of the cell.

Nerve cell is a long and has thread like branches.

Chloroplasts help in the synthesis of food by the process of photosynthesis.

Amoeba has no definite shape, and it keeps on changing its shape.

Red blood cell is spherical in shape.

Bacteria mycoplasma is the smallest cell measuring 0.1 micrometer.

The largest cell measuring 170 mm ×130 mm, is the egg of an ostrich.

There are different animal organs. Some of the names are Heart, Stomach, brain and lungs. Stem, Leaf, Roots etc are plant organs.

(a) Leaves are responsible for synthesis of food.

(b) Plant roots help in the absorption water and minerals.

Prokaryotic cell does not have a true nucleus.

Prokaryotic cell – Blue green algae

Eukaryotic cell – Onion peel cell

(a) Robert Hooke

(b) Cell

(c) protoplasm

(d) function

(e) 0.1; 0.5

(f) cell

(g) organs

(h) organism

(i) tissue

(j) organ system

The various parts of the cell are colorless and hence, difficult to distinguish. So, various stains are used to colour the parts of the cell to study the detailed structure through a microscope.

The dyes (stains ) which are used in the study of cell structure are methylene blue, dilute iodine solution, etc.

A tissue is a group of similar cells performing a specific function.

Examples – Epithelial tissue, muscle tissue.

A organ is a group of different tissues which work together to perform a specific function in the body of an organism.

Examples – Organs in the animal body - Brain and kidney

Organs in the plant body - Root and leaves.

Organ system – A group of closely related organs that work together to perform a specific function for the organism is called organ system.

(a) Muscular system and digestive system are examples of organ systems in animals.

(b) Root system and shoot system are main organ systems in plants .

(a) Heart – It pumps blood throughout the body.

(b) Brain – It controls the activities of other parts of the body.

(c) Roots – These help in absorption of water and minerals.

(d) Leaves – These are responsible for synthesis of food.

Red blood cells (RBCs) are usually spherical in shape. The main function of red blood cells is to carry oxygen from the lungs to the tissues around the body.

Prokaryotes have nuclear material without nuclear membrane whereas eukaryotes have well organized nucleus with a nuclear membrane.

Prokaryotes – Blue green algae and bacteria

Eukaryotes - Onion cells and cheek cells

Nerve cells (neurons) are long, branched and have thread-like projections so that they can connect other nerves cells and transmit messages over long distance

The other name of a nerve cell is neuron.

Most of cells are extremely small and cannot seen with naked eye, hence cells could not be observed and studied for thousands of years.

Two biologists, Schleiden (1839) and Schwann (1839) presented the cell theory. This stated that all the plants and animals are composed of cells and the cell is the basic unit of life.

Mitochondria is the site of cellular respiration or oxidation of food in a cell. It uses glucose and oxygen to produce energy. Hence, it is knowns as “Powerhouse of the cell”.

The function of nerve cell: The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body.

The muscle cells are responsible for movement in our body by contracting and relaxing.

The finger-like projection of varying lengths protruding out of the body of Amoeba, is called pseudopodia. These projections appear and disappear as Amoeba moves or feeds.

Thus, the function of pseudopodia is to facilitates movement and help in capturing food.

Chromosomes are thread-like structures usually present in the nucleus that become visible only during cell divisions.

The function of chromosomes is to transfer the characters from parents to the offsprings through the genes located on them.

Gene is a unit of inheritance in living organisms. It controls the transfer of a hereditary characteristic from parents to offspring. Genes are located on chromosomes.

Plastids are major organelles found only in plant cells. The green coloured plastids present in plant cells, are called chloroplast. It contains photosynthetic pigment called chlorophyll which helps in the synthesis of food.

The size of an ostrich egg is 170mm x 130 mm. It is the largest cell. It is a single cell called “fertilized egg cell” or “zygote”.

Cell wall provides shape and rigidity to the plant cell. It also provides protection the cell.

The cells which are found in animals are – Red blood cells (RBCs) and Muscle cells

The cells which are found in plants are – Xylem cells and phloem cells

Cytoplasm is a jelly-like substance present between the cell membrane and the nucleus. Cytoplasm contains many specialised cell organelles. Each of these organelles performs a specific function for the cell. Cytoplasm contains a number of minute living structure known as cell organelles. Each of these organelles performs a specific function for the cell.

Most of the chemical reactions which are necessary to keep cell alive take place in the cytoplasm.

Cell without its cell membrane is called Protoplasm. The Cytoplasm and Nucleus taken together make up the protoplasm.

The organisms made up of single cell are called unicellular organisms. Examples- Amoeba, Paramecium.

The organisms made up of many cells are called multicellular organisms. Examples- Animal and plant.

Chloroplasts are the green coloured plastids present in the cytoplasm of plant cells. They possess photosynthetic pigment called chlorophyll. Chlorophyll absorbs energy from the sunlight during the process of photosynthesis. In the process of photosynthesis, green plants make their own food in the presence of sunlight and chlorophyll with the help of inorganic substances like carbon dioxide and water. Thus, chloroplast help in the synthesis of food by green plants.

An Ameoba cell can change its shape and a white blood cell in human blood can also changing its shapes. The difference between an Amoeba cell and a white blood cell is that the Amoeba cell is a full-fledged organism which is capable of independent existence. While white blood cell is only a cell of human blood which is not a full-fledged organism and hence cannot exist independently. White blood cells can exist only inside the blood.

Amoeba cell and White Blood Cell both are eukarytic cell because they have well defined nucleuswith a nuclear membrane.

Differences between a plant cell and animal cell:

Mitochondria is the site of cellular respiration or oxidation of food in a cell. It uses glucose and oxygen to produce energy. Hence, it is knowns as “Powerhouse of the cell”.

Chromatin material is a tangled fibrous mass. The chromatin material condenses to form chromosomes during cell division.

The cell wall in onion peel cell is made of cellulose.

The group of similar cells which work together to perform a particular function is called tissue.

Nerve cells (neurons) are long, branched and have thread-like projections so that they can connect other nerves cells and transmit messages over long distance

Amoeba, yeast and rhizobium are examples of unicellular organisms while Yak is an example of multicellular organisms.

Chloroplasts are found only in those plant cells which carry out photosynthesis like the cells in green leaves. So, chloroplasts are not found in the root cells of a plant.

The correct answer is option (b) Nucleus.
Explanation: Nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring.

The basic similarity among all the living organisms is that they are made up of cells. Cell is the structural and functional unit of life.

The structural and functional unit of life called cell was discovered by Robert Hooke.

Red blood cell does not have a nucleus.

The correct option is B.

Explanation: The parts which are not present in an animal cell are cell wall and chloroplast. Plant cells have chloroplasts because they make their own food. Animal cells do not make their food, so there is no chloroplast. And, cell wall provides the stability and shape to the cell. Animal cells do not have cell walls because they don't need them.

The entire content of a living cell is known as protoplasm. It includes the cytoplasm and the nucleus. Protoplasm is called the living substance of the cell.

Epidermal cell is a plant cell while cartilage cell, neuron and epithelial cell are animal cells.

The largest cell measuring 170 mm ×130 mm, is the egg of an ostrich.

Cell wall is a characteristics of plant cell only and absent in animal cell. It is an outer, rigid, protective and supportive covering of plant cells. The cell wall lies outside of the plasma membrane. Epidermal cell and mesophyll cell are examples of plant cells. Thus, they have cell wall.

Organisms which do not have true nucleus are called prokaryotes. Bacteria and blue green algae are examples of prokaryotes.

Oesophagus is a part of human digestive system. It is a muscular tube which connects the pharynx to the stomach. It is also known as food pipe.

An amoeba cell and white blood cell present in human blood can change their shape.

The non-living part of a tomato cell is its cell wall. Cell wall is the outer most covering of a plant cell. It is a non-living and rigid.

(a) (i) The part P is Chloroplasts

Chloroplasts are the food producers in plant cells and they are not present in animal cells because animal cells do not make their own food.

(ii) The part Q is Cell wall

The cell wall is absent in the animal cells because they don't need cell walls. The main purpose of a cell wall is to provide stability and stiffness to the cell. And it is made up of cellulose.

(b) (i) The part R is Chlorophyll

Chlorophyll is the green pigment present in the leaves.

(ii) The part S is Cellulose

Cellulose is a fiber and wood, cotton, etc. all contain cellulose.

A is nucleus ; B is mitochondria; C is cell membrane ; D is cytoplasm; and E is chromosomes.

(a) (i) Eukaryotic cell (ii) Prokaryotic cell

(b) (i) Amoeba cell (ii) Bacterium cell

(a) The general name of the organelles X is plastids.

(b) (i) Chloroplasts (ii) green (iii) Chloroplasts (X) help in the synthesis of food by the process of photosynthesis.

(c) The colour of organells X which are present in the ripe fruits of tomato plant is red.

A is tissue; B is organ; and C is organ system.