Topic 1 - Cell biology (3)

Question 1

EXCHANGE SURFACES:
What do cells use diffusion for?
Give 2 examples

Answer 1

to take in substances they need and to get rid of waste products
1) oxygen and carbon dioxide are transfered between cells and the environment during gas exchange
2) urea diffuses from cells into the blood plasma for removal from the body by the kidneys

Question 2

EXCHANGE SURFACES:
What is urea?

Answer 2

a waste product produced from the breakdown of proteins

Question 3

EXCHANGE SURFACES:
How easy it is for an organism to exchange substances with their surroundings depends on what?

Answer 3

the organism’s surface area to volume ratio

Question 4

EXCHANGE SURFACES:
How are substances transpoted in and out of single celled organisms and why?

Answer 4

• gases and dissolved substances can diffuse directly into or out of the cell across the cell membrane
• because they have a large surface area compared to their volume so enough substances can be exchanged across the membrane to supply the volue of the cell

Question 5

EXCHANGE SURFACES:
Why can’t multicellular organisms only directly diffuse suctances in or out?

Answer 5

• they have a smaller surface area compared to their volume
• not enough substances can diffuse from their outside surface to supply the entire volume

Question 6

EXCHANGE SURFACES:
How do multicellulr organisms efficiently diffuse substances in and out?

Answer 6

• they have exchange surfaces for efficient diffusion
• they allow enough od the neccessary substances to pass through

Question 7

EXCHANGE SURFACES:
Name the 4 ways in which exchange surfaces are adapted to maximise effectiveness?

Answer 7

• they have a thin membrane, so substances only have a short distance to diffuse
• they have a large surface area so lots of substance can diffuse at once
• exchange surfaces in animals have lots of blood vessels, to get stuff into and out of the blood quickly
• gas exchange surfaces (e.g. alveoli) are often ventilated too - air moves in and out

Question 8

CHROMOSOMES AND MITOSIS:
In what form does the nucleus store genetic information?

Answer 8

chromosomes

Question 9

CHROMOSOMES AND MITOSIS:
What are chromosomes?

Answer 9

Coiled up lengths of DNA molecules

Question 10

CHROMOSOMES AND MITOSIS:
What do the different genes in chromosomes control?

Answer 10

the development of different characteristics e.g. hair colour

Question 11

CHROMOSOMES AND MITOSIS:
How many copies of each chromosome do body cell usually have?

Answer 11

2 - one from the mother and one from the father

Question 12

CHROMOSOMES AND MITOSIS:
How many pairs of chromosome are found in a normal human cell?

Answer 12

23 pairs of chromosomes

Question 13

CHROMOSOMES AND MITOSIS:
What is the cell cycle?

Answer 13

a series of stages where body cells in multicellular organisms divide to produce new cells

Question 14

CHROMOSOMES AND MITOSIS:
What is the name of the stage in the cell cycle where the cell divides?

Answer 14

mitosis

Question 15

CHROMOSOMES AND MITOSIS:
Why do multicellular organisms use mitosis?

Answer 15

to grow or replace cells that have been damaged

Question 16

CHROMOSOMES AND MITOSIS:
What is the result at the end of the cell cycle?

Answer 16

two new cells identical to the original cell with the same number of chromosmes

Question 17

CHROMOSOMES AND MITOSIS:
What are the 2 main stages in the cell cycle?

Answer 17

• Growth and DNA replication
• Mitosis

Question 18

CHROMOSOMES AND MITOSIS:
What is the DNA like in a cell that is not dividing?

Answer 18

the DNA is all spread out in long strings

Question 19

CHROMOSOMES AND MITOSIS:
What happens in growth and DNA replication?

Answer 19

• the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes
• it duplicates its DNA - so there’s one copy for each new cell. The DNA is copied and forms X-shaped chromosomes.
• each arm of the chromosome is and exact duplicate of the other (the left arem has the sam DNA as the right arm of the chromosome)

Question 20

CHROMOSOMES AND MITOSIS:
What happens in mitosis in the cell cycle

Answer 20

Once the contents and DNA have been copied, the cell is ready for mitosis
- the chromosomes line up at the centre of the cell and cell fibres pull them apart, the 2 arms of each chromosome go to opposite ends of the cell
- membranes form around the new sets of chromosomes. Theses become the nuclei of the two new cells - the nucleus has divided
- then the cytoplasm and the cell membrane divide
- the cell has produced two identical daughter cells, both with the same DNA as the parent cell

Question 21

MICROSCOPY:
What are stains used for?

Answer 21

to highlight objects in a cell by adding colour to them