Cells

Question 1

What are the differences between eukaryotic cells and prokaryotic cells

Answer 1

.Eukaryotes have no membrane bound organelles
.Smaller ribosomes in prokaryotes
.Prokaryotes have an unbound loop of DNA

Question 2

Describe the function of ribosomes

Answer 2

The site where proteins are synthesised in the cell.

Question 3

Describe the function of mitochondria

Answer 3

Produce ATP ( adenosine triphosphate ) for respiration etc.

Question 4

Describe the function of both variations of ER

Answer 4

Rough: folds and processes proteins that have been made by the ribosomes.
Smooth: synthesises and processes lipids.

Question 5

Name the constituents of the nucleus of a cell

Answer 5

Nuclear envelope
Nucleolus
Chromatin

Question 6

Name the organelle that contains digestive enzymes that hydrolyse invading cells or worn out components of the cell.

Answer 6

Lysosomes

Question 7

Describe the function of Golgi and how it transports substances.

Answer 7

Processes and packages lipids and proteins which are transported elsewhere by vesicles.

Question 8

Describe how epithelial cells are adapted for their function.

Answer 8

Large surface area which means greater diffusion of molecules into the cell due to villi that line the surface of the cell.
Large quantities of mitochondria due to high levels of respiration which requires ATP.
Villi have cells on them called micro villi to further increase the surface area.

Question 9

How are red blood cells adapted for transporting oxygen?

Answer 9

No nucleus so more space to bind oxygen

Question 10

What adaptation do sperm cells have in terms of transporting themselves?

Answer 10

They contain large amounts of mitochondria which produces ATP so the sperm cell can manouvre and propel its way through the female reproductive organs.

Question 11

How do you calculate magnification?

Answer 11

Magnification=length of image/length of actual specimen

Question 12

Name the three types of microscope

Answer 12

Light microscope
Transmission electron microscope
Scanning electron microscope

Question 13

Name the benefits for each type of microscope

Answer 13

Light: specimen image is in colour and if small enough can be live too.
TEM: higher resolution than the other microscopes
SEM: 3-D imaging

Question 14

How does a TEM work?

Answer 14

A beam of electrons is fired at the specimen using electromagnets to focus the beam. Denser parts of the specimen produce a darker image as they absorb more of the electrons. The image can then be viewed by a computer. Unfortunately it has to be done in a vacuum so no live specimens and it only works with a thin sample.

Question 15

How does a SEM work?

Answer 15

In a similar way to the TEM, the SEM scans the specimen using electrons to knock the electrons of the specimen. These are then received by a cathode ray to produce an image ( usually 3-D ). They are good for thick specimens but render lower resolution images and the specimen still can’t be alive.

Question 16

Describe homogenisation in cell fractionisation

Answer 16

Homogenisation: brakes up the cells in a very cold isotonic solution. Can be done by a vibrating the cells or in a blender to break down the plasma membrane to release the organelles into the solution. Has to be kept cold to reduce enzyme activity Which would break the organelles down. The isotonic solution stops organelles from shrinking or bursting as it has the same concentration of chemicals as the organelles.

Question 17

Describe filtration in cell fractionation

Answer 17

The homogenised solution is filtered through a gauze to separate large cell debris or tissue debris from the organelles. The organelles are small enough to pass through the gauze.

Question 18

describe ultracentrifugation in cell fractionation

Answer 18

The cell fragments that were collected from filtration are poured into a tube which is placed in the centrifuged and spun at different speeds. Lower speeds separate out the heavier organelles like the nucleus and mitochondria and faster speeds separate out the smaller organelles like ribosomes.
When each organelle is separated out the rest of the organelles are suspended in a liquid above the pellet known as the supernatant. This poured into another tube and then centrifuges again until all the organelles are separated out.