Cell Cycle

Question 1

What are the stages of the cell cycle?

Answer 1

Interphase- G1, S, G2

Mitosis- prophase, metaphase, anaphase, telophase, cytokinesis

Question 2

What happens during interphase?

Answer 2

G1- making new proteins and new organelles.
S- each chromosome is duplicated to become two chromatids, the cell checks itself.
G2- developing cell enlarges.

Question 3

What happens during prophase?

Answer 3

Chromosomes condense and become visible.
Each chromosome consists of two chromatids.
Centrioles move and the spindle starts to form.

Question 4

What happens during metaphase?

Answer 4

Nuclear envelope disappears.
Centrioles reach the pole and the spindle is completed.
Chromosomes are fully condensed.
Microtubules move centromeres to the equator.

Question 5

What happens during anaphase?

Answer 5

Spindle contracts and so the centromeres split.

Microtubules pull chromatids apart and towards the poles.

Question 6

What happens during telophase?

Answer 6

Chromatids are now separate chromosomes.
Chromosomes reach the poles.
Nuclear envelope forms.
Chromosomes decondense.

Question 7

What happens during cytokinesis?

Answer 7

The cell divides as does the nucleus.

Question 8

Define homologous with reference to chromosomes.

Answer 8

Having the same alleles at corresponding chromosomal loci.

Question 9

What are the three uses of mitosis?

Answer 9

Growth, repair/replacement and asexual reproduction.

Question 10

Why is mitosis important for growth?

Answer 10

Multicellular organisms need to produce new extra cells to grow. Each new cell has genetically identical to the parents cell, so it can perform the same function.

Question 11

Why is mitosis important for repair/replacement?

Answer 11

Damaged cells need to be replaced by new ones that perform the same functions and so need to the genetically identical to the parent cell.

Question 12

Why is mitosis important for a sexual reproduction?

Answer 12

Single celled organisms divide to produce two (identical) daughter cells that are separate organisms.
Some multicellular organisms produce offspring from parts of the parent plant.

Question 13

Explain the process of cell division using budding in yeast.

Answer 13

The nucleus divides by mitosis.
The cell swells on one side and bulges.
The nucleus, cytoplasm and organelles move into the bud and it pinches off as the cell wall forms so the bud becomes a separate cell.

Question 14

Outline meiosis.

Answer 14

For sexual reproduction special haploid cells (gametes) are produced.
When gametes fuse they form a zygote (a diploid cell) which can grow through mitosis.
Meiosis only happens at the sex cells of an adult organism.
During meiosis, only one version of each gene goes to a daughter cell.
Daughter cells of meiosis are genetically different.

Question 15

Define stem cell.

Answer 15

An undifferentiated cell that can specialise (by switching certain genes on/off into any other type of cell.

Question 16

How is an erythrocyte specialised?

Answer 16

Lots of haemoglobin to bind with oxygen.
Biconcave shape provides larger surface area for exchange and make the cell flexible to pass through capillaries.
No nucleus so there is more space for haemoglobin.

Question 17

How is a neutrophil specialised?

Answer 17

Lots of lysosomes to break down ingested pathogens.

Lobed nucleus the cell greater flexibility to make movement easier.

Question 18

How is a sperm cell specialised?

Answer 18

Flagellum, moving this rapidly gives the propulsion for movement toward the egg.
Acrosome containing many hydrolytic enzyme to penetrate the egg.
Many mitochondira to produce ATP for movement.

Question 19

How is a palisade cell specialised?

Answer 19

Large numbers of chloroplasts to capture sunlight for photosynthesis.
Transparent cell wall to allow sunlight through.
Chloroplasts circulate the cell to avoid heat damage to other organelles.

Question 20

How is a root hair cell specialised?

Answer 20

Large surface area for rapid absorption of water and mineral ions.

Question 21

How are guard cells specialised?

Answer 21

Outer wall is thinner than the inner wall, when light is shone onto them water moves in and makes them turgid- only the outer wall stretched creating a pore for gas exchange.
Vacuole- take up water and become turgid.
Many mitochondria to provide ATP for active transport.

Question 22

Outline differentiation with reference to neutrophils and erythrocytes.

Answer 22

Both originate from bone marrow.
Cells destined to become erythrocytes lose their nucleus, golgi apparatus and RER, they are filled with haemoglobin and become biconcave.
Cells destined to become neutrophils gain many lysosomes, mitochondria, golgi apparatus, RER, ribosomes, receptor sites on the cell surface membrane and many microtubules and microfilaments which form a well developed cytoskeleton.

Question 23

Outline differentiation with reference to xylem vessels and phloem sieve tubes.

Answer 23

Both originate from meristem cells .
Cells destined to become xylem vessels elongate and have the walls waterproofed by lignin deposits which kill the cell contents, the ends of the cell break down and they become long hollow tubes with wide lumen.
Cells destined to become phloem sieve tubes also elongate and lose most of their cytoplasm and nucleus but their ends to not completely break down and form sieve plates between the cells, each phloem cell has a companion cell next to it which keeps it alive.

Question 24

What is a tissue?

Answer 24

A tissue is a group of cells working together to perform a function.

Question 25

What is an organ?

Answer 25

An organ is a group of tissues working together to perform a function.

Question 26

What is an organ system?

Answer 26

An organ system is a group of organs working together to perform an overall life function.

Question 27

What are the four main types of tissue?

Answer 27

Epithelial- layers and linings.
Connective tissues- supports and holds structures together.
Muscle tissue- specialised to move body parts.
Nervous tissue- converts stimuli into electrical impulses and conducts those stimuli.

Question 28

Describe squamous epithelial tissue.

Answer 28

Flattened cells to form linings and walls e.g in blood vessels and alveoli held in place by the basement membrane which is made of collagen.

Question 29

Describe ciliated epithelial tissue.

Answer 29

Column shaped, an exposed surface covered in cilia which waft to move things (mucus, egg cells) through the body and can be found in tubes i.e bronchi and oviducts.

Question 30

Describe xylem tissue.

Answer 30

Consists of xylem vessel cell and parenchyma cells which fill the gaps between xylem vessels to provide support.

Question 31

Describe phloem tissue.

Answer 31

Consists of sieve tubes and companion cells which are highly metabolically active, moving products of photosynthesis up and down the phloem.