Cells

Question 1

Compare the structure of eukaryote and prokaryote cells

Answer 1

PROKARYOTE
No membrane-bound nucleus to store DNA (floats around in cytoplasm)
DNA isnt associated with proteins
No membrane-bound organelles
Cell wall made of murein
70s ribosomes

Eukaryote
It has a double membrane-bound nucleus
DNA is associated with histone bound proteins
Has membrane-bound organelles like mitochondria
Cell wall made of cellulose in plant cells
80s ribosomes

Question 2

Describe the structure and function of the nucleolus

Answer 2

Structure
Nucleus contains a double membrane and nuclear pores
Nucleus contains a dark staining region called the nucleolus
DNA wrapped in histone proteins

Function
Nucleus stores genetic information of the cell
Nucleolus produces rRNA which is used to make ribosomes

Question 3

Describe function and structure of mitochondria

Answer 3

Structure
Circular DNA
Double membrane-bound organelle
Folded inner membrane called cristae provide large surface area for enzymes involved with respiration
70s ribosomes

Function
Generate ATP for active processes like active transport

Question 4

Describe the rER

Answer 4

rER - Rough Endoplasmic Reticulum
Contains 80s ribosomes
Acts as a channelling system in the cell transporting materials like protein throughout the cell
Site of protein synthesis

Question 5

Describe the SER

Answer 5

SER - Smooth endoplasmic reticulum
No ribosomes
Synthesises lipids and steroids and transports them

Question 6

Describe the function of the Golgi body

Answer 6

Receives proteins from rER and lipids from SER
Modifies and processes proteins and lipids by adding a carbohydrate to them
Which are then packaged into vesicles to export out of the cell

Question 7

Describe the function of lysosomes

Answer 7

Hydrolyse cell walls of bacteria and old worn-out organelles to release the useful chemicals that they are made of

Question 8

Describe the function of the cell wall

Answer 8

Maintains shape of the cell gives it strength
Fully permeable to all molecules to stop it from bursting when it gains water by osmosis

Question 9

Describe structure and function of chloroplasts

Answer 9

Circular DNA
70s ribosomes
Contain thylakoids which stack to form grana which increase surface area to maximise absorption of light

Question 10

How does a TEM work

Answer 10

1. Electrons are transmitted through a thin section of the membrane
2. Electrons that are absorbed appear black and those which pass through appear bright
3. Electrons are detected by projecting them onto a fluorescent screen and taking a photo
4. A 2D back and-white image is produced by a computer with a resolution of 1nm

Question 11

How does SEM work

Answer 11

1. Electrons are scanned across the surface of the specimen
2. Electrons are scattered and bounce off the surface of the specimen
3. A computer analyses the electrons scattered and produces a 3D image of the surface of the specimen with a resolution of 10nm

Question 12

What are some limitations of a TEM

Answer 12

Living specimens cant be observed
Specimen must be very thin to allow electrons to pass through
Not in colour and 2D

Question 13

Outline the role of organelles in the production transport and release of proteins from eukaryotic cells

Answer 13

Proteins get produced at the rER using ATP generated by the mitochondria. The Golgi body modifies and processes the proteins by adding carbohydrates to them. These then get packaged into vesicles which transport the protein across the cytoplasm to the outer cell membrane to be released from the cell

Question 14

Describe the process of separating cell components

Answer 14

1. Cut tissue and grind in a blender to open up the cells
2. Filter the solution to remove and debris and any whole cells
3. Centrifuge at a slow speed which forms a pellet containing the nucleus
4. Extract supernatant and centrifuge at a higher speed to form a pellet containing smaller organelles like mitochondria and chloroplasts
5. Repeat the process to form pellets with even smaller organelles like Golgi body and ribosomes
6. Supernatant is now organelle free

Question 15

What are the 3 homogeniser solution properties

Answer 15

1. It Must be ice cold to slow down any enzyme activity that could damage organelles
2. Isotonic to keep the same water potential as the cell to prevent water from moving into the cell and bursting it
3. Must be buffered to maintain a constant pH to prevent enzymes from denaturing

Question 16

Why is the second centrifugation higher than the first

Answer 16

The first pellet formed contains a dense nucleus but smaller organelles like mitochondria and chloroplasts are less dense so must be done at higher speeds

Question 17

What is the cell membrane made up of

Answer 17

Phospholipids
Allow movement of non-polar molecules
Arranged to form a bilayer where hydrophilic heads point outwards and hydrophobic tails point inwards

Cholesterol
Adds strength to cell making it less fluid
Hydrophobic so prevents the loss of water from the cell

Proteins
Allow movement of polar molecules
Float within the bilayer where intrinsic proteins span the entire bilayer and where extrinsic proteins are on the surface of the bilayer

Glycoproteins
Proteins with a carbohydrate added to them
Function as receptors for intrinsic and extrinsic proteins
Allow cells to link to from tissues

Question 18

What are the 2 types of intrinsic protein and how do they transport molecules

Answer 18

Channel proteins have a water-filled channel which allows charged molecules to diffuse through, the charge of the channel protein determines which ions can enter

Carrier proteins
Have binding sites and can change shape
Molecules with a complementary shape attach to binding sites, proteins change shape to move molecules across the membrane, movement depends on the concentration of molecules on either side of the membrane

Question 19

What are 3 structural features found in all viruses

Answer 19

Attachment proteins
Protein coat
DNA/RNA

Question 20

Why are viruses describes as acellular and non living

Answer 20

Acellular because they don’t have a cell membrane and aren’t made out of cells
Non living because they have no metabolism so no reproduction and no respiration

Question 21

Describe the co-transport mechanism

Answer 21

Na+ is actively pumped out of the epithelial cells into the blood
This maintains a low concentration of Na+ ions inside the epithelial cells providing an inward diffusion gradient
Glucose and Na+ ions move and bind to the co-transport protein, each molecule has its binding site, the protein rotates and transports both molecules into the cytoplasm of the epithelial cell by facilitated diffusion
Glucose now has entered the blood by f.d. Na+ enters cell again by active transport

Question 22

What happens at interphase

Answer 22

DNA replicates and chromosomes are not visible

Question 23

What happens at prophase

Answer 23

Chromatin condenses to form chromosomes. 2 sister chromatids joined at the centromere

Question 24

What happens at metaphase

Answer 24

Chromosomes line up along the equator of the cell. Chromosomes attach to spindle fibres by their centromeres

Question 25

What happens at anaphase

Answer 25

Centromeres are split which allows chromatids to separate Spindle fibres contract and pull sister chromatids to opposite poles of the cell led by their centromere V shape forms