2.6 CELL DIVISION

Question 1

What is the cell cycle?

Answer 1

The cell cycle:
INTERPHASE-
growth 1 = cell grows, organelles replicate, other cellular processes occur
growth 1 checkpoint = checks for growth, nutrients, growth factor
synthesis = DNA replicated
growth 2 = cell continues to grow
growth 2 checkpoint = checks for cell growth, DNA replication and damage
MITOTIC PHASE
growth 0 = differentiate, senescence (damaged cells)
mitotic phase = mitosis, cytokinesis
spindle fibre assembly check = checks spindle fibres have attached to chromosome

Question 2

What is homologus chromosomes, haploid and diploid?

Answer 2

Homologus chromosomes are matching pairs of chromosomes- one inherited from each parent
Haploid- half the normal chromosome number- one chromosome of each type
Diploid- normal chromosome number- two chromosomes of each type (each inherited from different parent)

Question 3

What is mitosis used for?

Answer 3

Mitosis is used for growth, repair of tissues, cell replacement, asexual reproduction

Question 4

What are the stages of mitosis?

Answer 4

Stages of mitosis:
1. prophase- nuclear envelope disintegrates, centrioles begin to migrate to poles of cell, chromosomes condense and become visible, spindle fibres begin to form
2. metaphase- chromosomes line up along equator (metaphase plate)
3. anaphase- chromatids separate as spindle fibres pull chromosomes to poles of the cell
4. telophase- nuclear envelope reforms, chromosomes are now at poles of dividing cell, chromosomes decondense
CYTOKINESIS- division of cells by cytoplasm splitting (2 identical daughter cells formed)

Question 5

What is meiosis I?

Answer 5

Meiosis I (2 daughter nuclei formed with half number of chromosomes as parent nuclei)
1. early prophase I- chromosomes become more visible, centrioles replicate, chromosomes already replicated
1. mid prophase I- chromosomes fully condensed, homologus pairs pair up (bivalent)
1. late prophase I- CROSSING OVER (chromosomes preparing to break at specific point (chiasmata)), nuclear envelope disintegrates , spindles begin to develop
2. metaphase I- bivalents line up at equator of cell, centrioles arrive at poles, spindle fibres begin to attach to chromosome, crossing over still occurring, INDEPENDANT ASSORTMENT
3. anaphase I- WHOLE chromosomes move to poles, no division of centromeres, chiasmata splits
4. telophase I- nuclear envelope reforms, chromatids decondense/unravel to form chromatin
CYTOKINESIS- cytoplasm splits into 2 non-identical daughter cells

Question 6

What is meiosis II?

Answer 6

Meiosis II- chromatids separate (each haploid cell divides again to form 4 daughter haploid cells)
1. prophase II- chromosomes condense, nuclear envelope disappears, spindles develop, centrioles replicate
2. metaphase II- chromosomes line up individually at equator, spindle fibres attach to centromere, INDEPENDENT ASSORTMENT of chromosomes
3. anaphase II- chromatids separate to become chromosomes, spindle fibres pull them to the poles, become RANDOMLY SEGREGATED (randomly pulled apart)
4. telophase II- chromosomes decondense, nuclear envelope reforms, each cell has one chromosome from homologus pair
CYTOKINESIS- cytoplasm splits into 2 non-identical daughter cells

Question 7

Features of red blood cells.

Answer 7

Red blood cells (erythrocytes):
-transports oxygen
-no nucleus (more space for haemoglobin)
-packed full of haemoglobin (o2 binds)
-small and flexible (fit through capillaries, narrow lumen)
-biconcave shape- increases SA:V ratio

Question 8

Features of white blood cells.

Answer 8

White blood cells (neutrophils):
-immune system cell
-granular cytoplasm (contains digestive enzymes)
-multi-lobed nucleus (easier to fit through fenestrations in capillaries)

Question 9

Features of sperm cells.

Answer 9

Sperm cells:
-male reproductive cell (gamete)
-contains aerosome (digestive enzymes)
-haploid nucleus
-contains lots of mitochondria (generate ATP)
-flagellum (aid movement/locomotion

Question 10

Features of egg cells.

Answer 10

Egg cells:
-female reproductive cell (gamete)
-lots of cytoplasm (support many divisions, contains nutrients for embryo to grow)
-haploid nucleus

Question 11

Features of nerve cells.

Answer 11

Nerve cells:
-nervous system cell
-mylein sheath (insulates axon to speed up impulses)
-long and thin (carry rapid impulses)
-dendrite structure (branched, increase rate of nerve impulse transmission)

Question 12

Features of palisade cells.

Answer 12

Palisade cells:
-main site of photosynthesis
-box shaped (can be packed close together to increase surface area)
-cell wall (maintains rigidity)
-large vacuole (storage)
-move in cytoplasm (absorb maximum light)
-lots of chloroplasts (maximises rate of photosynthesis)

Question 13

Features of root hair cells.

Answer 13

Root hair cells:
-elongated structure (increases SA:V ratio)
-vacuole has low water potential (increase water absorption)
-maximise water (increases mineral uptake)

Question 14

Features of guard cells.

Answer 14

Guard cells:
-reveal stomata to enable gas exchange
-permeable to water (causes them to change shape)
-one side has a thicker cell wall (change shape asymmetrically)

Question 15

Features of squamous epithelia cells.

Answer 15

Squamous epithelia cells:
-found in alveoli, capillaries
-provide a thin pathway (short diffusion distance)
-flat (reduces friction, improves efficiency of liquid transport)

Question 16

Features of cilliated epithelia cells.

Answer 16

Cilliated epithelia cells:
-keeps airways free of mucus
-cillia (wafting mucus away from lungs through movement)
-lots of mitochondira (provides ATP)

Question 17

What are tissues, organs and organ systems?

Answer 17

Tissue- a collection of differentiated cells that have a specialised function/functions in an organism
Organ- a group of tissues in a living organism that have been adapted to perform a specific function
Organ system- a group of organs that work together to perform one or more functions

Question 18

Types of tissue.

Answer 18

Types of tissue:
cartilage- fibres of elastin and collagen that prevent ends of bones rubbing together and causing damage
squamous epithelia- squamous epithelia cells that form lining of lungs
muscle- skeletal muscle fibres that contract to move bonds to move parts of the body
cilliated epithelia- cilliated epithelia cells that line the trachea and allow mucus to be swept away from the lungs
plant epidermis- guard cells that reduce water loss and allows co2 in and out
phloem- sieve tube cells that allow the transport of organic nutrients from leaves and stems
xylem- vessel elements that allow the transport of water and minerals throughout plants

Question 19

What are stem cells and meristem cells?

Answer 19

Stem cells are undifferentiated cells with the potential to differentiate into a variety of specialised cell types of the organism
Meristem cells are undifferentiated cells that form meristematic tissue in plants, found at growth regions in plants

Question 20

What does undifferentiated and differentiated mean?

Answer 20

Undifferentiated- an unspecialised cell resulting from mitosis/meiosis
Differentiated- the process of a cell becoming differentiated. involves the selective expression of genes in a cells genomes

Question 21

What do stem cells do?

Answer 21

Stem cells:
-source of new cells which are essential for growth, development and tissue repair as they are able to undergo cell division again and again
-a renewing source of undifferentiated cells
-once a cell becomes specialised it loses the ability to divide (G0)
-speed of division needs to be controlled, too slow leads to aging, too fast leads to tumour development

Question 22

Where are stem cells found?

Answer 22

Stem cells found:
adult stem cells- already partly specialised (some genes switched off), e.g erythrocytes and neutrophils from stem cells in bone marrow
embryonic stem cells- completely specialised as they have all genes switched on, can form any type of cell
umbilical chord stem cells
plant meristem cells- production of xylem vessels and phloem sieve tubes from meristem cells

Question 23

What are the 3 levels of stem cells?

Answer 23

3 levels of stem cells:
(early embryos) totipotent- stem cells that can differentiate into any type of cell, a zygote and 8-16 cells from first set of mitotic divisions are totipotent, after this blastocyst forms
(late embryos) pluripotent- stem cells that can form all tissue types but not a whole organism, as they present in embryos and are the origin of different types of tissue within a component
(born) multipotent- stem cells that can only form a range of cells within a certain type of tissue, haematopoietic stem cells in bone marrow are examples

Question 24

What is meristematic tissue?

Answer 24

Meristematic tissue:
-meristem cells are formed within meristematic tissue
-this tissue is only found where plants are growing
- roots and shoots = apical meristems
- between xylem and phloem = vascular cambium
-pluripotency is continuous throughout a plants life

Question 25

Uses of stem cells.

Answer 25

Uses of stem cells:
-transplanted into specific areas to have the potential to treat certain diseases (e.g heart disease, spinal injuries)
-in diverse areas (e.g treat burns, drug trials)