Cells/Centrifugation

Question 1

What is the role of the nucleus?

Answer 1

It is the storage site of genetic information.
It is the site of DNA replication and it’s transcription to RNA (mRNA and tRNA). Manufactures ribosomal RNA and ribosomes.

Question 2

Parts of a prokaryotic cell that are not in a eukaryotic cell.

Answer 2

Cell wall, capsule, flagellum, circular DNA, plasmid, 70s ribosomes, cytoplasm.

Question 3

Plasmid

Answer 3

Small circles of DNA, used to exchange DNA between bacterial cells.

Question 4

Circular DNA

Answer 4

Contains genetic information to let cells replicate. Not associated with proteins.

Question 5

Mitochondria

Answer 5

They release energy.
They produce ATP.
They are the sites of the aerobic stages of respiration.
They have a double membrane to control the entry and exit of material.
Contain cristae - extensions of the inner membrane and provide a large surface area for enzymes in respiration to attach to.
Has a matrix which contains the enzymes for respiration.

Question 6

Cell wall

Answer 6

Made of murein.

Protects the cell against damage.

Question 7

Cytoplasm

Answer 7

Contains enzymes for metabolic reactions.

Question 8

Capsule

Answer 8

Thick polysaccharide layer outside of the cell for protection.
Also helps groups of bacteria stick together for more protection.

Question 9

Ribosomes

Answer 9

80s type in eukaryotes - bigger
70s type in prokaryotes
They make proteins - enzymes are also proteins.

Question 10

Flagellum

Answer 10

Tail for movement.

It helps spin the cell through fluids.

Question 11

Rough endoplasmic reticulum

Answer 11

Had ribosomes on it’s surface for protein synthesis.

Provides a pathway for transport of materials around the cell.

Question 12

Smooth endoplasmic reticulum

Answer 12

Makes, stores and transports lipids and carbohydrates.

Question 13

Comparing prokaryotic (bacteria) and eukaryotic cells - like for like

Answer 13

Bacteria don’t have a nucleus, a eukaryotes does.
Bacteria don’t have membrane bound organelles, eukaryotes do.
Bacteria don’t have mitochondria, eukaryotes do
Bacteria has 70s ribosomes, eukaryotes have 80s ribosomes (larger).
Bacterial cells have a murein cell wall, eukaryotes do not.
Bacterial cells are smaller than eukaryotes.
Bacteria have circular DNA, eukaryotes have linear DNA.
Bacteria might have capsules, eukaryotes don’t.

Question 14

Golgi Body

Answer 14

Modifies polypeptide chains into mature proteins.
Sorts and ships lipids for secretion.
Makes secretory enzymes.
Forms glycoproteins.
Modified proteins and lipids are transported in golgi vesicles.

Question 15

Lysosomes

Answer 15

Break down and recycle materials in the cell.

Contain proteases, lipase sand lysozymes.

Question 16

Centrifugation

Answer 16

Helps to separate organelles.
Most dense organelles are separated out first forming a pellet, which is removed. The supernatant contains other organelles which can be separated out when spun at a faster speed.

Question 17

Conditions needed of solution for centrifugation

Answer 17

Cold - slows down/stops enzyme activity to prevent the digestion of organelles.
Isotonic - prevents osmosis, so no lysis.
Buffer - prevents damage to enzymes. Maintains the pH.
Homogenised - to break open cells and release the contents. It is filtered to remove the larger cell debris.

Question 18

Steps in centrifugation

Answer 18

Chop up the cells. Homogenise the chopped up cells. Put in a cold, isotonic buffer solution. Filter the centrifuge filtrate. The nucleus makes up most of the pellet after being spun at a low speed. The centrifuge supernatant is spun at a higher speed to remove the less dense organelles. The next organelles could be mitochondria.

Question 19

Chloroplasts

Answer 19

They have a double plasma membrane which is highly selective
Grana - stacks of disc like structures called thylakoids. Chlorophyll is contained here for the first stage of photosynthesis.
Stroma - fluid filled matrix, for the second stage of photosynthesis. Starch grains are found here.

Question 20

Adaptions of epithelial cells for absorption

Answer 20

Microvilli for a large surface area.
Many mitochondria which release energy through active transport.
They have carrier proteins for active transport and facilitated diffusion.
Another adaption is that it has co-transport of sodium ions and glucose.
It has membrane bound enzymes to digest disaccharides to produce glucose.

Question 21

Cell wall (in plants, algae and fungi)

Answer 21

Plants - consists of micro fibrils of cellulose. Has a middle lamellae which is a thin layer that marks the boundary between adjacent cell walls and cements them together. It’s function is to provide mechanical strength and a pathway for water transport in the plant.
Algae - cellulose or glycoproteins or a mixture of both.
Fungi - do not contain cellulose but chitin, gly nss and glycoproteins.

Question 22

Cell vacuole (in plants)

Answer 22

A fluid filled sac bounded by a single membrane - tonoplast.
Contains salts, sugars.
It’s functions are to support, a temporary food store, pigments may colour petals - attract insects.