2.6 Cell Division And Diversity

Question 1

What happens in interphase?

Answer 1

G1 - growth of cells/organelles, increased number of organelles/protein synthesis
Synthesis - DNA replication
G2 - growth of cell/organelles/protein synthesis

Question 2

What happens at G0 checkpoint

Answer 2

Cell leaves the cycle temporarily or permanently if:
- the cell is fully differentiated
- The DNA is damaged (cells will repair DNA)

Question 3

G1 checkpoint

Answer 3

Ensure requirements (e.g. chemicals needed) for DNA replication are met

Question 4

G2 checkpoint

Answer 4

Check for mutations in DNA (daughter cells might not receive identical genetic information, proteins might not function)

Question 5

Metaphase checkpoint

Answer 5

Ensure chromosomes have attached to spindles correctly

Question 6

What is the role of mitosis?

Answer 6

Asexual reproduction
Repair of damaged cells/tissues
Growth of an organism

Question 7

Describe prophase

Answer 7

Nuclear envelope breaks down, chromosomes condense, spindle fibres form

Question 8

Describe metaphase

Answer 8

Chromosomes line up along equator of the cell, spindle fibres attach to the centromere of chromosomes

Question 9

Describe anaphase

Answer 9

Chromatids are pulled to opposite poles of the cell as spindle fibres contract breaking centromere

Question 10

Describe telophase

Answer 10

Nuclear envelope begins to reform, chromosomes uncoil, cell surface membrane undergoes cytokinesis, spindle fibres break down

Question 11

Describe cytokinesis

Answer 11

Davidson of the cytoplasm

Question 12

Describe mitosis and meiosis

Answer 12

Mitosis: production of two genetically identical diploid daughter cells
Meiosis: production of four genetically different haploid daughter cells (gametes)

Question 13

Define stem cells

Answer 13

Undifferentiated cells that can differentiate into specialised cells by dividing by mitosis

Question 14

Describe totipotent, pluripotent, multipotent and unipotent stem cells

Answer 14

Totipotent - differentiate into any type of cell including extraembryonic and placental cells

Pluripotent - can differentiate into any type of cell apart from extraembryonic and placental cells

Multipotent - can form more than one cell type of a particular lineage e.g. haematopoetic stem cells

Unipotent - give rise to one cell

Question 15

The role of meiosis

Answer 15

Genetic variation by crossing over and independent assortment
Independent assortment; in meiosis 1 and 2 the order in which chromosomes line up along the equator in metaphase is random
Crossing over (at chiasma); in prophase 1 homologous chromosomes form bivalents and maternal and maternal chromosomes exchange genetic material

Question 16

Describe how neutrophils are adapted

Answer 16

Defend the body against disease
- Flexible shape allows them to engulf foreign particles or pathogens
- Many lysosomes in their cytoplasm contain digestive enzymes to break down the engulfed particles
- Multilobed nucleus
- Attracted to and travel towards infection sites by chemotaxis

Question 17

Describe how erythrocytes are adapted to their function

Answer 17

Carry oxygen in the blood
Biconcave disc shape provides a large surface area for gas exchange
- No nucleus, mitochondria, endoplasmic reticulum and very little cytoplasm so more room for haemoglobin (protein that carries oxygen)
- Very small so large SA:V ratio
- Flexible because of their well developed cytoskeleton helping them to travel through narrow capillaries

Answer 18

• Cover the surfaces of organs
• Cells joined by interlinking cell membranes and a membrane at their base
• Ciliated epithelia have cilia that beat to waft particles away
• Squamous epithelia are very thin to allow efficient diffusion of gases

Question 19

Describe how sperm cells are specialised for their function

Answer 19

• Flagellum so they can swim to the egg
• Lots of mitochondria to provide energy to swim
• Acrosome (at the head of the sperm) contains digestive enzymes to enable the sperm to penetrate the surface of the egg
• Small but long and thin so they can move easily

Question 20

Where can stem cells be found in humans?

Answer 20

• Early embryos (can develop into any type of cell)
• In a few places in adults (can develop into a limited range of cells)
• Stem cells in umbilical-cord blood
• Induced pluripotent stem cells (iPs cells) developed in laboratories by reprogramming differentiated cells to switch on certain key genes and become undifferentiated

Question 21

Uses of stem cells

Answer 21

Replace damaged cells
- Treat neurological disorders e.g. Parkinson’s and Alzheimer’s
- Developmental biology e.g. how organisms grow and develop, help us understand about cancer and developmental disorders
- Bone marrow transplants
- Drug research

Question 22

Define tissue, organ, organ system

Answer 22

Tissue - group of specialised cells working together to carry out a function
Organ - group of tissues working together to carry out a function
Organ system - a number of organs working together to perform an overall life function