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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

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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
Q

Metaphase 2 of Meiosis

A

Chromosomes attach by their centromere to the spindle

Chromatids randomly arranged

26
Q

Anaphase 2 of Meiosis

A

Centromeres divide

Chromatids pulled apart by motor proteins that drag them along the tubulin threads of spindle to opposite poles

Chromatids randomly segregated

27
Q

Telophase 2 of Meiosis

A

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
Q

How Meiosis produces genetic variation

A

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
Q

Why multicellular organisms need specialised cells

A

Large

Smaller SA/V ratio

Most cells not in contact with external environment

Needs specialised cells to carry out particular functions

30
Q

Genome=

A

Genetic material within an individual

31
Q

Gene pool=

A

All the genetic material within a population

32
Q

🌟Erythrocytes (RBCs) adaptations

A

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
Q

🌟Neutrophils (phagocytes) adaptations

A

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
Q

🌟Spermatozoa adaptations

A

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
Q

Epithelial cells adaptations

A

Flattened - short diffusion distance

May have cilia - can waft substances

36
Q

Palisade cells adaptations

A

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
Q

Guard cells: How they work

A

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
Q

🌟Root hair cells adaptations

A

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
Q

Xylem vessel adaptations

A

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
Q

Phloem adaptations

A

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
Q

Companion cells adaptations

A

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
Q

4 main tissue types

A

Epithelial

Connective

Muscle

Nervous

43
Q

Meristematic tissue

A

Thin walls - little cellulose

No chloroplasts

No large vacuole

Can undergo Mitosis to differentiate

44
Q

How cambium cells differentiate into xylem vessels

A

Lignification

Ends of cells break down

Continuous column formed

45
Q

How cambium cells differentiate into sieve tubes or companion cells

A

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
Q

Stem cells

A

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
Q

Sources of stem cells

A

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
Q

Potential uses of stem cells

A

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
Q

🌟Organisation of cells in multicellular organisms

A

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
Q

🌟The cell cycle

A

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
Q

🌟Mitosis

A

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
Q

🌟Mitosis compared w meiosis

A
  • 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
Q

🌟Cell division and budding of yeast cells

A
  • 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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