Cells Biology A level

Question 1

State and define the term Cell.

Answer 1

The basic unit of all living organisms, it is surrounded by cell surface membrane and contains genetic material DNA and cytoplasm containing organelles.

Question 2

What is an organelle? Give one example

Answer 2

A functionally and structurally distinct part of the cell e.g ribosome.

Question 3

State the difference between Eukaryote and prokaryote.

Answer 3

An organism whose cells contain a nucleus and other membrane bound organelles are known as Eukaryotes whereas prokaryotes are organism whose cells do not contain nucleus or any membrane bound organelles.

Examples for Eukaryotes: Plants and animals
Examples for Prokaryotes: Bacteria

Question 4

Plant and animal seen under the light microscope.

Question 5

State th comparison between the plant and animal cells.

Answer 5

Both are living cells. They both have a nucleus. They both have a cell membrane. They both have a mitochondria. They both are small cell which are seen in microscope by naked eye.
Differences:
Only plant cell consist of cell wall whereas animal cell has permeable cell membrane.
Only plant cell has chloroplast.
Plant cell has large central vacuole with tonoplast whereas animal cell has small radicle cell vacuoles.

Question 6

what is meant by magnification?

Answer 6

the times the image is bigger than the original size of the object. with help of eyepiece and objective lens.

Question 7

Define the term Resolution

Answer 7

It is the minimum distance between the two substance that can be differentiated as two.
The maximum resolution of light microscope is 200 nm and electron microscope is 0.5 nm. The lower the resolution the more clearer the picture.

Question 8

Name the two types of electron microscope and state their difference.

Answer 8

The two types of EM microscope are Scanning Electron microscope and Transmission Electron microscope. SEM electron beams are used to scan the surfaces of structures and reflected beam is observed whereas TEM electrons are passed through the specimen before being viewed. This allows us to see thin sections of specimens, and thus to see inside living cells.

Question 9

State the difference between light and electron microscope.

Answer 9

The form of radiation in light microscope is light wave and in electron microscope is electron beam. The wavelength of radiation in light 400-700 nm and in electron is 0.005. the types of lenses in light is glasses and in the other is electromagnetic. The specimen is living/dead and electron is non living. There are coloured dyes in light and metallic dyes used in electron microscope. The image produced in light is real image whereas in electron it is virtual.

Question 10

The role of cell membrane seen under the electron microscope.

Answer 10

Cell membrane seen under the electron microscope is trilaminar and protective in nature. It is semi permeable and controls cell movements.

It plays important role in cell recognition antigens. It plays role in cell signaling (reception).
Harmone gives signal for function.

Question 11

The role of nucleus when viewed under EM microscope.

Answer 11

It controls all activities in cell. It plays important role in cell division also in cell synthesis. It consists of genetic material which helps in inheritance. The chromatin which consists of DNA are called histones and is known as heterochromatin. The chromatin with no DNA is known as Euchromatin.

Question 12

Function of mitochondria.

Answer 12

It is the site of aerobic respiration. The food is oxidized to release ATP. It consists of double membrane and it’s base is known as matrix. The inner membrane is folded and known as cristae where there are stalk particles found which consists of enzymes that play role in food respiration.

Question 13

The role of endoplasmic reticulum and types of endoplasmic reticulum.

Answer 13

They are network of flattened sacs and are the ways for travelling the materials across cell. (cytoplasm). It is continuous with the outer membrane of the nuclear envelope.The types are smooth and rough endoplasmic reticulum.

Question 14

Role of rough endoplasmic reticulum

Answer 14

They give attachment to ribosomes. So is a site of protein synthesis.

Question 15

Role of smooth endoplasmic reticulum.

Answer 15

It helps in making of lipids and steroid hormones. Example is cortisol, progesterone.

Question 16

Function of ribosomes. (Detail)

Answer 16

It helps in protein synthesis. It consists of two subunits The bigger and the smaller subunit. The space in-between these two units is for the attachment of messenger RNA coming from the nucleus via the nuclear pore and attaches to ribosome for protein synthesis.

Question 17

Function of microtubules. (Detail).

Answer 17

It is the Long straw hollow structures. Essential for base and support. They form a criss cross structure and form skeleton of Cell. They are the small tubules that make up cytoskeleton of the cell.
Note: the microtubules for centrioles are in round circle.

Question 18

How are the microtubule are formed?

Answer 18

There are two types of protein in cell. The alpha and beta tubulin. They combine to form dimer. They fix and make sheet. The sheet becomes hollow and it becomes microtubule.

Question 19

Significance of microtubles. (Functions)

Answer 19

They help in cell division mitosis. Microtubules are located in all cell where movement is required.
Fot ex. In centrioles, spindle fibre, flagella and sperm tail.

Question 20

What is the golgi apparatus and define golgi vesicles.

Answer 20

It is an organelle found in eukaryotic cells the golgi apparatus consists of stack of flattened sacs constantly forming at one end and breaking up into golgi vesicles at the other end.

The golgi vesicles carry their contents often to the cell surface membrane for secretion the golgi apparatus chemically modifies the molecules it transports. E.g sugars may be added to proteind to make glycoproteins.

Question 21

Functions of golgi apparatus.

Answer 21

Golgi vesicles are used to make lysosomes.
Sugars are added to proteins to make molecules known as glycoproteins. Sugars are added to lipids to make glycolipids. Glycoproteins and glycolipids are important component of membranes and ate important molecules in cell signaling.
During plant division, golgi enzymes are involved in syntheses of new cell walls.

Question 22

Define the term of lysosomes.

Answer 22

a special organelle found in eukaryotic cells, it contains hydrolytic enzymes and has a varety of destructive functions, such as removal of old cell organelles.

Question 23

Functions of lysosomes.

Answer 23

Lysosones can engulf and destroy unwanted cell components, such as molecules or organelles, located inside the cell.
Endocytosis
Exocytosis
self digestion

Question 24

function of cilia.

Question 25

Function of flagella

Question 26

function of cell wall in plant cell

Answer 26

The cell wall is made up of a carbohydrate known as Cellulose. It gives high tensile strength which supports the cell. It is fully permeable and gives the cell its fixed shape. It maintains the osmotic pressure and gives the cell protection.

Question 27

What is plasmodesmata and what is its role in plant cell?

Answer 27

It is the gap between the two cell walls. It is via one cell communicates with other.

Question 28

describe what does the structure of chloroplast consist of?

Answer 28

It has the presence of a double membrane.
it has the presence of 70 s ribosome.
it has presence of circular DNA.
they have ability to divide and ability to make proteins.
They have thylakoid a flattened membrane bound fluid filled sac which is the site of the light dependent reactions of photosynthesis in a chloroplast.

Question 29

What is bacteria?

Answer 29

Bacteria is a group of single celled prokaryotic microorganisms they have a number of characteristics such as ability to form spores. which distinguish from other prokaryotes such as Archea.

Question 30

Features in bacteria that are always present?

Answer 30

They have a cell wall containing a strengthening material called peptidoglycan. The cell wall protects the bacterium and is essential for survival.
Like all cells, have cell surface membrane.
It has circular DNA
it has 70 s ribosomes.

Question 31

The structures that are sometimes present in a bacterium cell.

Answer 31

It consists of flagellum for locomotion, very simple structure. (it is for the motality of bacteria)
They have capsule or slime layer which is for additional protection. Bacteria makes capsule and becomes dormant. It waits untill suitable environment.
Mesosomes are cell membrane infolding and form important centres for various activities.
ex. photosynthesis centre and nitrogen fixation.
plasmid small circle of DNA which may help in antibiotic resistance.
pili are anchoring points (attachement to other cells or surfaces; involved in sexual reproduction.

Question 32

what is the difference between vertical and horizontal transmission.

Question 33

Give me 4 simmilarities and 8 differences between prokaryotic and Eukaryotic cells.

Answer 33

Both have a cell surface membrane, both have ribosomes, both have a cytoplasm.
They both are living and have genetic material DNA.
The differences are:
Eukaryotic cell have nucleus, prokaryotic does not have a nucleus.
In Eukaryotes, there is 80 s ribosomes present whereas in prokaryotes there are 70 s ribosomes present.
In prokaryotes, cell wall made up of peptidoglycan (a polysaccharide) made up of amino acids.
In eukaryotes, cell wall sometimes present and made up of cellulose or lignin.
In prokaryotes, cell divison by binary fission whereas eukaryotes by mitosis or meosis.

Question 34

Define the term virus and write a 5 mark note on virus

Answer 34

a very small infectious particle that can replicate only inside living cells; it consists of DNA OR RNA surrounded by protein coat; the outer lipid envelope may also be present.