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OCR AS/A Level Biology A > Module 2.6 Cell Division, Cell Diversity and Cell Differentiation > Flashcards

Module 2.6 Cell Division, Cell Diversity and Cell Differentiation Flashcards

1
Q

Purpose of checkpoints in the cell cycle

A

To prevent uncontrolled division

To detect and repair damaged DNA

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2
Q

M phase

A

A checkpoint chemical triggers condensation of chromatin

1/2way through the cycle, the metaphase checkpoint ensures that the cell is ready to complete mitosis

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3
Q

Events within cell during M phase

A

Cell growth stops

Nuclear division = PMAT

Cytokinesis

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4
Q

Gap 0 phase

A

A resting phase triggered during early G1 at the restriction point by a checkpoint chemical

Some cells e.g. epithelial cells in the gut don’t have this phase

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5
Q

Events within cell during Gap 0 phase

A

Cells may undergo apoptosis, differentiation or senescence

Some cells e.g. neurones remain in this phase almost indefinitely

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6
Q

Gap 1 phase

A

A G1 checkpoint control mechanism ensures the cell is ready to enter S phase and begin DNA synthesis

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7
Q

Events within the cell during Gap 1 phase

A

Cells grow

Cells inc. in size

Transcription occurs

Organelles duplicate

Biosynthesis e.g protein synthesis

Enzymes made which are needed for DNA replication in the S phase

P53 helps control this phase

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8
Q

S phase of interphase

A

Every molecule of DNA replicated (chromosomes unwound, DNA is diffuse)

Specific sequence for replication (housekeeping first and normally inactive genes replicated last)

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9
Q

Events within the cell during S phase

A

Now committed to cell cycle

DNA replicates

Chromosomes consist of identical sister chromatids

Rapid phase to reduce chance of spontaneous mutations happening

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10
Q

G2 phase of interphase

A

Special chemicals ensure the cell is ready for Mitosis by stimulating proteins that will be involved in making chromosomes condense and in the formation of spindle

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11
Q

Events within the cell during G2 phase

A

The cell grows

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12
Q

What is Mitosis used for?

A

Asexual reproduction

Growth

Tissue repair

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13
Q

Prophase during Mitosis

A

Chromosomes (consisting of 2 identical sister chromatids) shorten and thicken - DNA supercoils

Nuclear envelope breaks down

Centriole in animal cells breaks down - 2 new daughter centrioles move to opposite poles

Spindle forms

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14
Q

Metaphase during Mitosis

A

The pairs of chromatids attach to the spindle threads - attach by their centromeres

Chromosomes @equator

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15
Q

Anaphase during Mitosis

A

Centromere of each pair of chromatids splits

Motor proteins along the tublin threads pull each sister chromatid in a pair in opposite directions

Chromosomes assume a V shape

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16
Q

Telophase during Mitosis

A

Separated chromosomes reach the poles

New nuclear envelopes form around the sets of chromosomes

Cells contain 2 nuclei each

Genetically identical to each other and the parent

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17
Q

Cytokinesis in animals

A

The plasma membrane folds inwards and “nips in” the cytoplasm

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18
Q

Cytokinesis in plants

A

An end plate forms where the equator of the spindle was, and new plasma membrane and cellulose cell wall material are laid down on either side along this end plate

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19
Q

Meiosis produces

A

Haploid gametes

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20
Q

Prophase 1 of Meiosis

A

Chromatin condensed

Each chromosome supercoils

Nuclear envelope breaks down

Spindle threads of tubulin protein form from the centrioles (in animal cells)

Chromosomes in homologous pairs

Crossing over - alleles shuffled

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21
Q

Metaphase 1 in Meiosis

A

Crossing over

Homologous chromosomes attach to the spindle threads by the centromere

Independent assortment

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22
Q

Anaphase 1 in Meiosis

A

Homologous chromosomes pulled apart by motor proteins that drag them along the tubulin threads of spindle

Centromeres DON’T divide

Each chromosome consists of 2 chromatids

Alleles shuffled

23
Q

Telophase 1 in Meiosis

A

In most animal cells:
2 new nuclear envelopes form around each set of chromosomes then cytokinesis and a short interphase whilst the chromosomes uncoil

In most plant cells:
The cell goes straight from anaphase 1 to prophase 2

24
Q

Prophase 2 in Meiosis

A

Nuclear envelopes break down

Chromosomes coil and condense

Each chromosome consists of 2 chromatids

Chromatids NOT identical

Spindle forms

25
Metaphase 2 of Meiosis
Chromosomes attach by their centromere to the spindle Chromatids randomly arranged
26
Anaphase 2 of Meiosis
Centromeres divide Chromatids pulled apart by motor proteins that drag them along the tubulin threads of spindle to opposite poles Chromatids randomly segregated
27
Telophase 2 of Meiosis
Nuclear envelopes form around each of the 4 haploid nuclei In animals, 2 cells divide to give 4 haploid cells In plants, a tetrad of 4 haploid cells is formed
28
How Meiosis produces genetic variation
Crossing over during prophase 1 shuffles alleles Independent assortment of chromatids in anaphase 1 - random distribution of maternal and paternal chromosomes Independent assortment of chromatids in anaphase 2 Haploid gametes produced - can undergo random fusion with gametes derived from another organism of the same species
29
Why multicellular organisms need specialised cells
Large Smaller SA/V ratio Most cells not in contact with external environment Needs specialised cells to carry out particular functions
30
Genome=
Genetic material within an individual
31
Gene pool=
All the genetic material within a population
32
🌟Erythrocytes (RBCs) adaptations
No nucleus and most organelles absent - max. space for haemoglobin to inc. oxygen carrying capacity V small Large SA/V ratio - O2 can diffuse easily Biconcave disc shape - inc. SA/V ratio for oxygen exchange = more efficient uptake of oxygen into RBCs No nucleus and organelles = flexible - can travel through v narrow capillaries Filled w haemoglobin - can bind to oxygen to form oxyhaemoglobin to transport it to aerobically respiring cells
33
🌟Neutrophils (phagocytes) adaptations
Travel towards infected sites by chemotaxis Ingest bacteria and some fungi by phagocytosis Contain a lot of lysosomes containing lysin enzymes to digest pathogens Multi-lobed nucleus - can fit between gaps in endothelial cells of capillaries to leave blood Contain many mitochondria - to move lysosomes and phagosomes through the cell along microtubules
34
🌟Spermatozoa adaptations
Many mitochondria - aerobic respiration, ATP so flagella/undulipodium can move Haploid nucleus - when it fertilises the egg the zygote will be diploid Small, long and thin - can move easily Acrosome - enzymes digest the outer protective covering of the ovum so the spermatozoon can penetrate the egg so it can fertilise it
35
Epithelial cells adaptations
Flattened - short diffusion distance May have cilia - can waft substances
36
Palisade cells adaptations
Adapted for photosynthesis because: Long, cylindrical, closely packed but small air spaces for CO2 to diffuse into cells Large vacuole - chloroplasts nearer the periphery of the cells, reduces diffusion distance for CO2 Many chloroplasts- for photosynthesis Contain cytoskeleton threads and motor proteins to move chloroplasts (up in low sunlight, down in high sunlight)
37
Guard cells: How they work
Light energy used to produce ATP ATP actively transports potassium ions from surrounding epidermal cells into the guard cells Water potential lowered Water enters guard cells from neighbouring epidermal cells via osmosis Guard cells swell Tips of cellulose cell wall - more flexible Thicker = more rigid Tips bulge, stoma enlarges Gas exchange can occur CO2 diffuses in for photosynthesis Steep concentration gradient maintained O2 can diffuse out
38
🌟Root hair cells adaptations
Hair like projections - inc. surface area/larger surface area for osmosis and mineral uptake (active transport) into the roots Mineral ions actively transported in - water potential lowered, water moves in via osmosis down the water pot. grad. Many carrier proteins in the membrane - for active transport of mineral ions Thin wall = short diffusion path Many mitochondria = energy for active transport of minerals Many channel proteins - for water uptake via osmosis
39
Xylem vessel adaptations
Continuous hollow tubes (no contents) - less resistance to water flow, more space Walls impregnated with lignin - strengthens walls (prevents collapse), waterproofs wall (reduces lateral movement of water), Increases adhesion - increases capillarity Spiral pattern of lignin - flexibility Bordered pits - allows lateral movement of water to get around a blockage Narrow lumen - more effective capillary action
40
Phloem adaptations
Small cytoplasm + most organelle absent - less resistance, more space Sieve plates - allows sucrose through Joined end to end to form tube - continuous transport Bi-directional flow - sucrose can go up and down Living - active processes can take place
41
Companion cells adaptations
Lots of mitochondria - lots of respiration, allows active processes to occur e.g. active loading of sucrose into sieve tubes Nucleus - controls companion cell and sieve tube element Plasmodesmata - allows continuation of cytoplasm between companion cell and sieve tube element
42
4 main tissue types
Epithelial Connective Muscle Nervous
43
Meristematic tissue
Thin walls - little cellulose No chloroplasts No large vacuole Can undergo Mitosis to differentiate
44
How cambium cells differentiate into xylem vessels
Lignification Ends of cells break down Continuous column formed
45
How cambium cells differentiate into sieve tubes or companion cells
Sieve tubes: most organelles lost ,sieve plates develop Companion cells: retain organelles, continue metabolic processes to provide ATP for active loading of assimilates into the sieve tubes
46
Stem cells
Undifferentiated Pluripotent Can express all their genes Can divide by Mitosis to provide more cells that can differentiate into specialised cells for growth and repair
47
Sources of stem cells
Embryonic stem cells In umbilical cord blood Adult stem cells in infants and children e.g in the blood, brain, muscle, bone, adipose tissue and skin Induced pluripotent stem cells (iPS cells) - developed in labs
48
Potential uses of stem cells
Bone marrow transplants Cancer treatment Drug research Developmental biology Potential to repairing damaged tissues/replace lost tissues E.g. Alzheimer's, Parkinsons, diabetes, burns, hearing loss, arthritis
49
🌟Organisation of cells in multicellular organisms
Cells differentiate Groups of similar specialised cells working together to perform a common function = tissues Groups of tissues working together = organs Groups of organs working together = organ systems
50
🌟The cell cycle
Interphase: - G1, S and G2 phases - G1 - cell grows, respires, proteins made, organelles replicated - S - DNA replication occurs, chromosomes become sister chromatids joined by a centromere - G2 - DNA replication is checked for mistakes, organelles replicated Mitosis: - Prophase - sister chromatids supercoil, nuclear envelope breaks down, spindle fibres form - Metaphase - sister chromatids line up on the equator, spindle fibres attach to centromere - Anaphase - spindle fibres shorten + pull sister chromatids apart towards opposite poles - Telophase - chromosomes uncoil, nuclear envelope reforms Cytokinesis: - Cytoplasm cleaves down furrow to split cytoplasm - 2 genetically identical daughter cells produces (identical to each other and the parent cell)
51
🌟Mitosis
Prophase: - Sister chromatids supercoil and shorten and thicken - Sister chromatids consist of sister chromatids joined by a centromere - Now visible under a light microscope - Nuclear envelope breaks down - Centriole divides in 2 - each daughter centriole goes to a pole - Spindle fibres (microtubules) begin to form Metaphase: - Sister chromatids line up along the equator - Spindle fibres attach to the centromeres Anaphase: - Centromere splits - Chromatids separate - Spindle fibres shorten - Pull identical chromatids to opposite poles w centromeres leading Telophase: - Chromosomes uncoil - Nuclear envelope reforms - Spindle fibres break down
52
🌟Mitosis compared w meiosis
- Mitosis produces 2 genetically identical diploid daughter cells used for growth and repair. Occurs in all body cells and involves only one division - Meiosis produces 4 genetically different haploid daughter cells and produces gametes. Only occurs in the ovaries and testes and involves two divisions
53
🌟Cell division and budding of yeast cells
- Nuclei divide by mitosis - Bulge in surface of the cell - Nucleus moves into bulge - Bulge pinches off - Uneven cytoplasm distribution between the two cells

OCR AS/A Level Biology A (14 decks)

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