Chapter 6 - Cell division

Question 1

Chromatids

Answer 1

2 identical copies of DNA held together at a centromere

Question 2

Cyclins

Answer 2

the chemical signal that triggers the movement from one phase to another

Question 3

G1 Phase

Answer 3

➜ First growth phase
➜ Organelles replicate, and cell grows in size
➜ Biosynthesis - protein, enzyme & RNA synthesis
➜ P53- helps control G1 phase
↳ tumour suppressor

Question 4

G1 Checkpoint

Answer 4

➜ If cell passes requirements it is triggered to begin DNA replication
➜ If not it enters G0 phase
➜ Checked for:
* cell size
* nutrients
* growth factors
* chromosome damage

Question 5

S Phase

Answer 5

➜ DNA replicates (known as synthesis of DNA)
➜ Sister chromatids formed after chromosomes duplicates
➜ rapid phase - DNA susceptible to mutagenic agents

Question 6

G2 Phase

Answer 6

➜ Second growth phase - prepares for mitosis
➜ Cell continues to increase in size
➜ Energy stores increased
➜ Chemicals stimulate proteins that will be involved in condensing chromosomes
➜ production of tubulin protein = used to make microtubules for spindle

Question 7

G2 Checkpoint

Answer 7

➜ End of G2 phase before mitotic phase
➜ If checkpoint passed, cell initiates the molecular processes that signal mitosis
➜ Checks for:
* Cell size
* DNA replication
* DNA damage

Question 8

Mitotic Phase

Answer 8

➜ mitosis = nucleus divides
➜ cell growth stops

➜ cytokinesis = cytoplasm divides and 2 genetically identical daughter cells produced

Question 9

Cytokinesis

Answer 9

➜ follows M phase
In animal cells, cell surface membrane pinches inwards creating a cleavage furrow in the middle of the cell which contracts, dividing the cytoplasm in half
In plant cells, vesicles from the Golgi apparatus gather along the equator of the spindle, vesicles merge with each other to form the new cell surface membrane and secrete a layer of calcium pectate which becomes the middle lamella. Layers of cellulose are laid upon the middle lamella to form the primary and secondary walls of the cell
End product: 2 haploid cells

➜ cytokinesis = cytoplasm divides and 2 genetically identical daughter cells produced

Question 10

ₘᵢₜₒₛᵢₛ Prophase

Answer 10

➜ Chromatin condense to form chromosomes
➜ Centrioles move to opposite ends of cell
➜ Forms a network of protein microtubules = spindle fibres
➜ Nuclear envelope breaks down

Question 11

ₘᵢₜₒₛᵢₛ Metaphase

Answer 11

➜ No longer has nuclear membrane
➜ chromosomes line up at equator
➜ spindle fibres attach to the kinetochores of the chromosomes

➜ Chromosomes attached in the middle of cell on the spindle fibres by the centromeres

Question 12

ₘᵢₜₒₛᵢₛ Anaphase

Answer 12

➜ Centromeres divide
➜ Spindles contract and shorten
➜ Chromatids move to opposite ends of the spindle
➜ Makes chromatids V shaped

Question 13

ₘᵢₜₒₛᵢₛ Telophase

Answer 13

➜ Chromosomes uncoil and decondense
➜ Nuclear envelope reforms and spindle fibres break down
➜ Nucleolus formed
➜ Cytokinesis occurs causing cytoplasm to split into 2 identical daughter cells

Question 14

significance of mitosis

Answer 14

➜ damaged tissue replacement
➜ cells die = replace those (growth)
➜ some animals regenerate body parts
➜ unicellular zygotes (zygote divides by mitosis) to grow into multicellular organisms

Question 15

Mitosis in plant cells

Answer 15

➜ growth in plants occur in meristems
➜ root tip meristem found behind the protective root cap
➜ pre prepared slides of root tips can be studied - using squash technique

Question 16

Asexual reproduction

Answer 16

➜ the production of new individuals of a species by a single parent organism
➜ offspring = genetically identical to parent

Question 17

ₘₑᵢₒₛᵢₛ Ⅰ - Prophase Ⅰ

Answer 17

➜ DNA condenses and become visible as chromosomes
➜ Homologous chromatids pair up forming bivalents
➜ This is crossing over
➜ point at which crossing over occurs = chiasma (chiasmata = plural)
➜ Centrioles move to opposite ends and form spindle fibres
➜ Nuclear envelope disintegrates

Question 18

ₘₑᵢₒₛᵢₛ Ⅰ - Metaphase Ⅰ

Answer 18

➜ bivalents assemble along equator of spindle fibres by centromere
➜ This is independent assortment

Question 19

ₘₑᵢₒₛᵢₛ Ⅰ - Anaphase Ⅰ

Answer 19

➜ Spindle fibres contract
➜ bivalents pulled to opposite poles and chromatids stay joined to each other (centromeres do not divide)
➜ one chromosome goes to opposite ends
➜ This is genetic variation

Question 20

ₘₑᵢₒₛᵢₛ Ⅰ- Telophase Ⅰ

Answer 20

➜ Nuclear membrane reforms
➜ Chromatin uncoil
➜ Cytokinesis occurs and divides into 2 genetically varied haploid cells from diploid cells

Question 21

ₘₑᵢₒₛᵢₛ Ⅱ - Prophase Ⅱ

Answer 21

➜ Nuclear envelope breaks down
➜ chromosomes condense
➜ Centrioles move to opposite ends and form spindle fibres at a right angle to the old one

Question 22

ₘₑᵢₒₛᵢₛ Ⅱ - Metaphase Ⅱ

Answer 22

➜ Individual chromosomes assemble in middle of cell via their centromere
➜ Independent assortment again and genetic variation

Question 23

ₘₑᵢₒₛᵢₛ Ⅱ - Anaphase Ⅱ

Answer 23

➜ Spindle fibres contract
➜ Centromeres divide and individual chromatids are pulled to opposite poles
➜ creates four groups of chromosomes

➜ Individual chromosomes pulled to opposite ends of cell

Question 24

ₘₑᵢₒₛᵢₛ Ⅱ - Telophase Ⅱ

Answer 24

➜ Chromosomes uncoil and form chromatin again
➜ Nuclear membranes form around each group of chromosomes and nucleolus becomes visible
➜ Cytokinesis occurs forming 4 haploid daughter cells which are genetically different.

Question 25

Significance of Meiosis

Answer 25

➜ crossing over - swapping of alleles can result in new combination of alleles
➜ independent assortment - different combos of chromosomes in daughter cells increase genetic variation between gametes

Question 26

erythrocytes

Answer 26

➜ biconcave - increase surface area
➜ cytoplasm has high amounts of haemoglobin
➜ no nucleus is present so more space inside cell
➜ elastic membrane allows cell to be flexible and change shape as it squeezes through narrow capillaries

Question 27

Neutrophils

Answer 27

➜ have a flexible shape that allows them to squeeze through cell junctions in capillary wall
➜ flexibility also enables them to form pseudopodia (cytoplasmic projections) that engulf microorganisms
➜ large number of lysosomes present in the cell
➜ flexible nuclear membrane further helps cell to penetrate cell junctions - causes lobed nucleus

Question 28

Sperm cells

Answer 28

➜ head contains a nucleus that contains half the normal number of chromosomes
➜ acrosome in the head contains digestive enzymes
➜ mid-piece is packed with mitochondria to release energy for tail movement
➜ tail rotates, propelling the sperm cell forwards

Question 29

Root hair cells

Answer 29

➜ root hair to increase surface area
➜ thinner walls than other plant cells so that water can move through easily
➜ permanent vacuole contains cell sap which is more concentrated than soil water, maintaining a water potential gradient
➜ Mitochondria for active transport of mineral ions
➜ no chloroplast

Question 30

Ciliated epithelium

Answer 30

➜ have cilia which beat in a coordinated way to shift material
➜ goblet cells secrete mucus

Question 31

Squamous epithelium

Answer 31

➜ consists of a single layer of flattened cells on a basement membrane
➜ layer of cells forms a thin cross-section which reduces the distance = short diffusion distance
➜ permeable, allowing for the easy diffusion of gases

Question 32

Palisade cells

Answer 32

➜ large number of chloroplasts to maximise absorption of light
➜ tall and thin shape of the cells allows light to penetrate deeper before encountering another cell wall

Question 33

Guard cells

Answer 33

➜ Inner cell walls are thicker
➜ outer cell walls are thinner
➜ difference in the thickness of the cell walls allows the cell to bend when turgid
➜ cytoplasm has a high density of chloroplasts and mitochondria

Question 34

Muscle cells

Answer 34

➜ All muscle cells have layers of protein filaments
➜ high density of mitochondria
➜ skeletal, smooth and cardiac

Question 35

Totipotency

Answer 35

stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells

Question 36

Pluripotency

Answer 36

stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells

Question 37

Multipotency

Answer 37

stem cells that have the capacity to develop into types present in a specific tissue or organ

Question 38

erythropoiesis

Answer 38

As red blood cells lack a nucleus, they cannot divide, meaning that new erythrocytes are constantly being formed from bone marrow stem cells in order to maintain the red blood cell count in the blood

Question 39

Cambium

Answer 39

➜ the stem cells at the inner edge of the cambium differentiate into xylem cells and the stem cells at the outer edge of the cambium differentiate into phloem cells
➜ Cambium cells that differentiate to form the xylem lose their cytoplasm, deposit lignin in their cell walls and lose their end cell walls
➜ Cambium cells that differentiate to form the phloem lose some of their cytoplasm and organelles, and develop sieve plates

Question 40

Alzheimers disease

Answer 40

➜ common cause of dementia which leads to memory loss and the loss of other cognitive abilities
➜ stem cells can be used to grow nerve cells - has potential to repair neurological condition

Question 41

Parkinsons disease

Answer 41

➜ shaking, stiffness and slowness of movement in people with parkinsons disease is due to death of dopamine - producing brain cells
➜ stem cells could be used to replace these dopamine producing cells