NOTES PREPARED BY
ASHAQ HUSSAIN BHAT
TEACHER SCHOOL
EDUCATION DEPARTMENT
JAMMU AND KASHMIR
CHAPTER 16
The Cell: Structure and Functions
SUMMARY
•All organisms consist of smaller parts are called organs.
•All organs have still smaller parts. The smallest living part of an organism is 'Cell',
•Cells were first observed in cork by Robert Hooke in 1665.)
•Cells exhibit variety of shapes and sizes.
•Number of cells also varies from organism to organism.
•Some cells are big enough to be seen with the unaided eye e.g.hen's egg.
•Some organisms are single-celled while others contain large number of cells.
•Single cell in unicellular organisms performs all the basic functions performed by a variety of cells in multicellular organisms.
•The cell has three main parts, the cell membrane, cytoplasm, which contains smaller parts called organelles, and the nucleus.
•Nucleus is separated from cytoplasm by a nuclear membrane.
•Cells without well organised nucleus, i.e. lacking nuclear membrane, are called prokaryotic cells.
•Plant cells differ from animal cells in having an additional layer over the cell membrane termed cell wall.
•Coloured bodies called plastids are found in the plant cells only.Green plastids containing chlorophyll are called chloroplasts.
•Plant cell has a big central vacuole, unlike a number of small vacuoles in animal cells.
KEYWORDS
•Cell: Basic structural unit of living organisms.
•Multicellular: Made of more than one cell,il
•Unicellular: Made up of a single cell.
•Pseudopodia: False feed, projections of varying length protruding out of Amoeba body.
•Tissue : A group of similar cells performing a specific function.
•Cell Membrane: Separates the inside contents of the cell from the surrounding medium.ideos
• Cytoplasm : Fluid present between the cell membrane and the nucleus.
•Cell Wall: Outer thick layer of cell.
• Organelles : Various components present in the cytoplasm.
•Prokaryotic Cells: Cells having nuclear material without nuclear membrane.
•Eukaryotic Cells: Cells having well organised nucleus with a nuclear membrane.
•Vacuole: Empty space in the cytoplasm.
•Plastids : Small coloured bodies scattered in the cytoplasm.
• Chloroplasts: Green coloured plastids.
TEXTBOOK EXERCISE
Q.1 Define a cell?
Ams. A cell is the basic unit of living things.
02 Who discovered the cell?
Ams. Robert Hook discovered the Cell.
Q3. Give three examples of unicellular organisms?
Ams. Algae, Acetabularia and Amoeba etc.
Q4. Answer the following questions:
i.Why cells could not be discovered before 17th century?
Ans. The Cells could not be seen before the 17th centuary because of their small size.
(ii) Why cork could not be observed as such by Hook?
Ans.Cork could not be observed, as such because it is a solid structure and made of box, like; compartments, forming a honeycomb structure.
(ii) Where did Hook demonstrate his observations on the cork slice?
Ans. He demonstrated his work to scientist at Royal Society of London.
(iv) Name the outmost layer of an animal cell?
As. Cell membrane is the outmost layer of an animal cell.
(v) Name the layer which is present outside the plasma membrane in plant cell?
Ans. Cell wall is present outside the plasma membrane in plant cell.
(vi) Where are Chromosomes present in a cell?
Ans. Chromosomes are present in nucleoplasm in a cell.
(vii) Name the cell part that has tiny holes?
Ans. Cell Membrane has tiny holes.
(viii) Name the cell organelles, which are found in the plant cell?
Ans. Mitochondria, chloroplasts, endoplasmic reticulum, golgi complex, lysosomes, ribosomes are the cell Organelles, which are found in the plant cell.
(ix) Name the cells having branched structure?
Ans. Nerve cells having branched structure.
(x)Which cell can be observed with the unaided eye?
Ans. An Ostrich's egg is the cell, which can be observed with the unaided eye.
Q.5. Mention the functions of the following:
(a) Cell Membrane
(a) The functions of cell membranes are :
(i) It protects the cell.
(ii) It provide shape to the cell.
(iii) It allows materials to enter and leave the cell through the tiny holes.
(b) The functions of chromosomes are:
(i) Transmission of characters from one generation to another.
(ii) Controls all the life functions taking place inside the cell.
Q.6. Why are the following important to a plant cell?
(i) Cell Wall
(ii) Chloroplast
(iii) Mitochondria
(iv) Nucleus
Ans. The importance of these are :
(i) Cell Wall
(a) It provides rigidity to the cell.
(b) It provides protection to the cell.
(b) Controls all the life functions taking place inside the cell.
(ii) Chloroplast: Green coloured plastids are chloroplasts. They are commonly known as "Kitchen of the cell' because chloroplasts are the site of photosynthesis i.e. process of making food,
(iii) Mitochondria: It is also called power house of the cell because mitochondria help in release of energy from food, as well as, store energy.
(iv) Nucleus: (a) Nucleus transmits characters from one generation to the another.
Q7 Draw an outline diagram of an animal cell. Label the different
Q.8. Mention three differences Between plant cell and animal cell?
Ans. Plant cells differ from animal cells. Differences between them are:
Plant Cell
(i) Plant Cells have cell wall, made up of cellulose.
(ii) Plant Cells have chloroplasts.
(iii) Plant Cells have thin cytoplasm.
(iv) Large vacuoles are present.
(v) Centrosome is absent
(vi) Reserve food is in the form of starch.
Animal Cell
(ii) Chloroplasts are absent.
(iii) Animal cells have thick cytoplasm.
(iv) Vacuoles are absent.
(v) Centrosome is present.
(vi) Reserve food is in the form of glycogen.
Q.9. What features are possessed by, both, plant cells and animal cells?
Ans. The Cell Membrane, the cytoplasm and the nucleus are possessed by both plant cells and animal cells.
Q.10. Why are nerve cells long? Why do these cells have projections?
Ans. The nerve cells are long and branched and has thread like projections, as it has to convey message to different parts of the body.
Q.11. Why are mitochondria known as the Power house of the cell'?
Ans. Mitochondria is known as the 'Power house of the cell' because it is site of oxidative breakdown of glucose in aerobic cell respiration to produce energy rich ATP molecules. One mole of glucose, in aerobic respiration, produces 36 ATP molecules. In other words, we can say that it performs the functions of respiration, and provide the cell with energy that is why it is regarded as 'Power house of the cell'.
Q.12. Which four basic elements constitute more than 20% of protoplasm?
Ans. Carbon, hydrogen, nitrogen and oxygen are the four basic elements constitute more than 90% of protoplasm.
Q.13. Write in brief about the variation in shape and size of cells?
Ans. Plant and animal cells are differ in size and shape. Some cells are visible to the naked eye. Most cells, however, are visible only with a microscope. For example, an ostrich egg is the largest animal cell. In plants, some algae have very big cells i.e. an algae, Acetabularia is about ten centimeter in length, but Fibres in plants, like; jute and hemp are a few centimetres. In our body, nerve cells are the largest and some blood cells are the smallest. Some cells, like those of amoeba and white blood cells of our body continuously change their shapes. A nerve cell is long branched, because it has to convey message to different parts of the body. In other words, the shape at cell is related to its function.
Q.14. Name the different cell organelles and the functions of these organelles?
Ans. Mitochondria, chloroplasts, endoplasmic reticulum, golgi complex and lysosomes are the different organelles. There functions are as :
Organelles. Their Functions
1.Mitochondria. Perform the function of respiration, provide
the cell with energy.)
2. Chloroplast. Help in food manufacture (photosynthesis)
3.Endoplasmic. It provides a large surface area for life functions to reticulum take place.
4.Golgi complex It collects and distributes the substances made in the cell. Synthesis and secretion of many materials.
5.Lysosomes. Contain enzymes which help in breathing down or destroying the various materials.
Q.15. What is meant by protoplasm? How does it differ from cytoplasm?
Ans. Ninety nine percent of protoplasm by weight is made up of four elements, namely, carbon, hydrogen, nitrogen and oxygen.
Protoplasm includes the cell membrane, the cytoplasm and the nucleus. It is made up of carbon, hydrogen, nitrogen and oxygen.
The cytoplasm is a jelly, like; substance occupying most of the space inside the cell. All the life functions take place in the cytoplasm. It occupies the space between the cell membrane and other nucleus.
Q.16. Fill in the blanks, using the words given below:-
(Mycoplasma, Microscope, Nucleus, Ostrich egg, Cytoplasm, Lysosome, Mitochondria, Robert Hook, Plant,Cell Memberane)
(1)The .................is also called as suicide bags.
(ii)The term 'cell' was given by.............
(iii) The instrument used to see tiny objects is called a..................
(iv)Smallest cell is that of a.................
(v)An.......... is a cell that can be seen without a microscope.
(vi)The............... , ................... And..............are the parts of a cell.
(vii) Energy is produced in.................
(viii) Cell wall is present in..........cells.
Ans. (i) Lysosome; (ii) Robert Hook; (iii) microscope; (iv) mycoplasma; (v) Ostrich egg: (vi) Cell membrane, Cytoplasm, nucleus;(vii) mitochondria; (viii) Plant.
Q.17. Write 'True' or 'False' in front of the statement given below:
1.Most of the cell is the nucleus. ( )
2.Only the nucleus of a cell represents the protoplasm. ( )
3.Most cells are microscopic. ( )
4. All living organisms are made of cells. ( )
5.Energy cell has cytoplasm. ( )
6.All cells in a multicellular organism can live independently. ( )
7. The outermost covering in an animal cell is called cell wall. ( )
Ans. (1) True; (ii) False; (iii) True; (iv) True; (v) True; (vi) True; (vii) False
Q.18. Match the statements in column A with those in column B.
Ans
Column A Column B
Cell. . Unit of living body
Nucleus. Boss of the cell
Cell Wall. Outermost covering in plant cells.
Chloroplast. Photosynthesis
Cytoplasm. Jelly like substance between cell
Organelles. Tiny structures inside cells.
Q.19. Label the different parts numbered 1 to 6 of the cell indicated by guidelines in the figure shown below:
SHORT ANSWER TYPE
Q.1. Give the main features of nerve cell.
Ans. The main features of nerve cell are:
(1)This tissue forms the brain, spinal cord and nerves.
(ii)Each cell is called neuron.
(iii) Neuron is a cell specialized to conduct impulses.
(iv) Each neuron consists of a cell body or cyton and a long rod like structure called axon.
Q.2. Give the main functions of plasma membrane.
Ans. Plasma membrane is also called as cell membrane. The main functions of plasma membrane are :
(i) It protects the cell and organelles.
(ii) It provides shape to the cell.
(iii) Being semi-permeable, it regulates selectively the entrance and exit of substances.
(iv) It regulates various excretions.
Q.3. Give the main functions of nucleus.
Ans. The main functions of nucleus are :
(i) It controls all vital activities of the cell.
(ii) It helps in cell division.
(iii) It carries hereditary information's from one generation to the other generation.
Q.4. Where are chromosomes found in a cell? State their function.
Ans. Nucleus contains hair like structures called chromosomes. These carry genes and help inheritance or transfer of characters from the parents to the offspring.
Q.5. "Cells are the basic structural units of living organisms. Explain.
Ans. Organisms living world differ from one another but all are made up of cells. So, cell in the living organisms are basic complex living structures.
Q.6. Explain why chloroplasts are found only in plant cells?
Ans. Green coloured plastids are called chloroplasts. They provide green colour to the leaves and chlorophyll in the chloroplasts of leaves is essential for photosynthesis. In human cell, it is not required. So, chloroplasts are found only in plant cells.
Q.7. Whether the cells in an elephant are larger than cells in a rat.
Ans. The size of the cells, infact, has no relation with size of the body of the animal or plant. It is not necessary that the cells in the elephant will be much bigger than those in a rat. The size of the cell is related to its function. For example, nerve cells, both in the elephant and rat, are long and branched. They perform the same function of transferring messages.
Q.8. All plants have cell wall. Why do they need them ?
Ans. Cell wall i.e. additional layer surrounding the cell membrane is required by the plants for protection. Plant cells are exposed to the environment and need protection against variations in temperature, wind, velocity, atmospheric moisture etc.
Q.9. If the structure of the nucleus is the same in cells of plants,animals and bacteria.
Ans. No, the nucleus of the bacterial cells is not well organised like the som cells of multicellular organism. Plant cell has cell wall while animal cells do not.
Q.10. What do you understand by multicellular and unicellular organisms? Discuss with examples.
Ans. Organisms made of more than one cell are called multicellular
Examples: Birds, ants, man etc.
Organisms made up of a single cell are called unicellular.
Examples: Amoeba, Paramecium.
Q.11. From which part of body, multicellular and unicellular organisms perform functions ?
Ans. The single-celled organism like amoeba takes and digests food, respires, excretes, grows and reproduces with the help of only one cell. Similar functions in multicellular organisms are carried out by groups of specialised cells forming different tissues which in turn form organs.
LONG ANSWER TYPE QUESTIONS
Q.1. Describe the variations in shape and size of cells.
Ans. Generally cells are round, spherical or elongated. Some cells are long and pointed at both ends. They exhibit spindle shape. Cells sometimes are quite long. Some are branched, like; the nerve cell or a neuron. The nerve cell receives and transfers messages, there by helping to control and coordinate the working of different parts of the body.
Components of the cell are enclosed in a membrane. This membrane provides shape to the cells of plants and animals. Cell wall is an additional covering over the cell membrane in plant cells. It gives shape and rigidity to these cells. Bacterial cell also has a cell wall.
The size of cells in living organisms may be, as small as, a millionth of a metre or may be, as large as, a few centimetres. However, most of the cells are microscopic in size and are not visible to the unaided eye. They need to be enlarged or magnified by a microscope. The smallest cell is 0.1 to 0.5 micro metre (um) in bacteria. The largest cell measuring 170 mm x 130 mm is the egg of an ostrich.
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