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Biology A-Level -James > Chapter 2.6-Cell division, cell diversity and cellular organisation > Flashcards

Chapter 2.6-Cell division, cell diversity and cellular organisation Flashcards

1
Q

What is mitosis?

A

type of nuclear division that produces daughter cells genetically identical to each other and to the parent cell

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2
Q

What is cytokinesis?

A

cytoplasmic division following nuclear division, resulting in two new daughter cells

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3
Q

What is interphase?

A
  • phase of cell cycle where the cell is not dividing; it is subdivided into growth and synthesis phases
  • G1, S and G2 phase
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4
Q

What happens at G1(gap 1) phase of the cell cycle of interphase?

A
  • cell grows and increases in size
  • transcriptions of genes to make RNA occurs
  • organelles duplicate
  • biosynthesis
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5
Q

What happens in the S (synthesis) phase of interphase?

A
  • once the cell enters this phase, it is committed to finishing the cell cycle
  • DNA replicates
  • phase is rapid because the espoused DNA base pairs are more susceptible to mutagenic agents, this reduces the chances of spontaneous mutations happening
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6
Q

What happens in the G2 (gap 2) phase of interphase?

A

cell grows

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7
Q

What happens in the G0 (gap 0) phase of interphase?

A
  • apoptosis (programmed cell death), differentiation or senescence
  • some type of cells, such as neurones, remain in this phase for a very long time or indefinitely
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8
Q

What are the purpose of checkpoints in the cell-cycle?

A
  • prevent uncontrolled division that would lead to tumours (cancer)
  • detect and repair damage to DNA (e.g. caused by UV light)
  • the cycle cannot be reversed
  • the DNA is only duplicated once during the cell cycle
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9
Q

Where are the two main checkpoints in the cell cycle?

A
  • G2/M checkpoint

- G1/S checkpoint (restriction point)

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10
Q

What happens at the G2/M checkpoint?

A

chemicals stimulate spindle-forming proteins

  • checkpoint chemical triggers condensation of chromatin
  • metaphase checkpoint ensures proper separation of sister chromatids
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11
Q

What happens at the G1/S checkpoint?

A
  • ensures that the cell is ready to enter S phase

- some cells (triggered by a checkpoint chemical enter G0)

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12
Q

What does the p53 gene do in the cell cycle?

A
  • triggers the two main checkpoints in the regulation of the cell cycle
  • it is known as the tumour suppressor gene
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13
Q

Why do living organisms need to produce genetically identical daughter cells by mitosis?

A
  • Asexual reproduction: single-celled protoctists such as Amoeba and Paramecium divide by mitosis to produce new individuals. Other organisms which do this are strawberry’s, fungi and some female sharks kept in captivity without any males have produced females identical to themselves
  • Growth: all multicellular organisms grow by producing more cells that are genetically identical to each other and to the parent cell from which they arose by mitosis.
  • Tissue repair: wounds heal when growth factors, secreted by platelets and macrophages (white blood cells) and damaged cells of the blood-vessels walls, stimulate proliferation of endothelial and smooth muscle cells to repair damaged blood vessels
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14
Q

What is the anagram to remember the stages of mitosis?

A
  • Peas Make Awful Tarts

- prophase, metaphase, anaphase and telophase

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15
Q

What happens at prophase in mitosis?

A
  • chromosomes that have replicated during the S phase of interphase and consist of two identical sister chromatids, now shorten and thicken as the DNA supercoils.
  • nuclear envelope breaks down
  • centrioles divide and the two new daughter centrioles move to opposite poles of the cell
  • cytoskeleton protein (tubulin) threads form a spindle between these centrioles.
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16
Q

What happens at the metaphase in mitosis?

A
  • the pair of chromatids attach to the spindle threads at the equator region
  • they attack by their centromeres
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17
Q

What happens at the anaphase in mitosis?

A
  • the centromere of each pair of chromatids splits
  • Motor proteins, walking along the tubular threads, pull each sister chromatid of a pair, in opposite directions, towards opposite poles
  • Because their centromere goes first, the chromatids, now called chromosomes, assume a V shape.
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18
Q

What happens at the telophase in mitosis?

A
  • the separated chromosomes reach the poles
  • a new nuclear envelope forms around each set of chromosomes
  • The cell now contains two nuclei each genetically identical to each other and to the parent cell from which they arose.
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19
Q

What happens during cytokinesis in animal cells?

A

-plasma membrane folds inwards and ‘nips in’ the cytoplasm

-

20
Q

What happens during cytokinesis in plant cells?

A
  • end plate forms where the equator of the spindle was

- new plasma membrane and cellulose cell-wall material are laid down on either side along this end plate

21
Q

What is meiosis?

A

type of nuclear division that results in the formation of cells containing half the number of chromosomes of the parent cell

22
Q

What are diploid cells?

A
  • body cells (somatic/autosomal)

- contain 2 sets of chromosomes

23
Q

What are haploid cells?

A
  • sex cells (gametes)

- having only one set of chromosomes; represented by the symbol ‘n’

24
Q

What happens during fertilisation?

A

two haploid cells fuse therefore the cell then has the correct number of chromosomes (2n)

25
Q

What are homologous chromosomes?

A

matching chromosomes, containing the same genes at the same place (loci). They may contain different alleles for some of the genes

26
Q

What happens at prophase 1 of meiosis?

A
  • chromatin condenses and each chromosome supercoils.
  • nucelar envelope breaks down, and spindle threads of tubular protein form from the centriole in animal cells
  • the chromosomes come together in their homologous pairs
  • each member of the pair consists of two chromatids
  • crossing over occurs when non-sister chromatids wrap around each other and may swap section so that alleles are shuffled
27
Q

What happens at metaphase 1 of meiosis?

A
  • the pairs of homologous chromosomes, still in their crossed state, attach along the equator of the spindle
  • Each attaches to a spindle thread by its centromere
  • the homologous pairs are arranged randomnly , with the members of each pair facing opposite poles of the cell. This is called independent assortment
  • the way that they line up in metaphase determines how they will segregate independently when pulled apart during anaphase.
28
Q

What happens at anaphase 1 of meiosis?

A
  • member of each pair of homologous chromosomes are pulled apart by motor proteins that drag them along the tubular threads of the spindle
  • the centromeres do not divide, and each chromosome consists of two chromatids
  • the crossed-over areas separate from each other, resulting in swapped areas of chromosomes and allele shuffling
29
Q

What happens at telophase 1 of meiosis?

A
  • two nuclear envelopes form around each set of chromosomes, and the cell divides by cytokinesis. There is a short interphase when the chromosomes uncoil.
  • each new nucleus contains half the original number of chromosomes, but each chromosome consists of two chromatids
  • plant cells go straight from anaphase 1 into prophase 2.
30
Q

What happens at prophase 2 of meiosis?

A
  • if nuclear envelopes have reformed, they now break down
  • the chromosomes coil and condense, each one consisting of two chromatids
  • the chromatids of each chromosome are no longer identical, due to crossing over in prophase 1
  • spindle forms
31
Q

What happens at metaphase 2 of meiosis?

A
  • chromosomes attach, by their centromere, to the equator of the spindle
  • the chromatids of each chromosome are randomly arranged
  • the way that they are arranged will determine how the chromatids separate during anaphase
32
Q

What happens at anaphase 2 of meiosis?

A
  • centromeres divide
  • chromatids of each chromosome are pulled apart by motor proteins that drag them along the tubular threads of the spindle, towards opposite poles
  • the chromatids are therefore randomly segregated
33
Q

What happens at telophase 2 of meiosis?

A
  • nuclear envelopes form around each of the 4 haploid nuclei
  • in animals, the two cells now divide to give 4 haploid cells
  • in plants, a tetrad of four haploid cells is formed
34
Q

How does meiosis produce genetic variation?

A
  • crossing over during prophase 1 shuffle alleles
  • independent assortment of chromosomes in anaphase 1 leads to random distribution of maternal and paternal chromosomes of each pair
  • independent assortment of chromatids in anaphase 2 leads to further random distribution of genetic material
  • haploid gametes are produced, which can undergo random fusion with gametes derived from another organism of the same species
35
Q

What is differentiation?

A

process by which stem cells become specialised into different types of cell

36
Q

What are erythrocytes?

A

red blood cells that carry oxygen from the lungs to respiring cells

37
Q

How are erythrocytes adapted to carry out their function?

A
  • very small so have a large SA:V ratio. This means that oxygen can diffuse across their membranes and easily reach all regions inside the cell. Biconcave shape
  • flexible, well developed cytoskeleton allows the erythrocytes to change shape so that they can twist and turn, as they travel through very narrow capillaries.
  • most of the organelles are lost at differentiation, so they have no nucleus, mitochondria or endoplasmic reticulum. This means there is more room for the many haemoglobin molecules housed inside them
38
Q

What are neutrophils?

A

type of white blood cell that is phagocytic (can ingest microbes and small particles)

39
Q

Where are both neutrophils and erythrocytes derived from in the body?

A

stem cells in the bone marrow

40
Q

How do neutrophils work?

A
  • attracted to and travel towards infection sites by chemotaxis
  • ingest bacteria and some fungi by phagocytosis
  • they are about twice the size of erythrocytes, and each neutrophil contains a multi lobed nucleus.
41
Q

What are spermatozoa?

A

sperm cell

42
Q

How are spermatozoa specialised to carry out their function?

A
  • many mitochondria carry out respiration. The ATP provides energy for the undulipodium (tail) to move and propel the cell towards the ovum
  • long and thin allows them to be able to move easily
  • once it reaches the ovum, enzymes are released from the acrosome (specialised lysosome). The enzyme digests the outer protective covering of the ovum, allowing the sperm head to enter the ovum
  • head contains the haploid male gamete nucleus and very little cytoplasm.
43
Q

What are epithelial cells?

A

cells that constitute lining tissue

44
Q

What are the features of epithelial cells?

A
  • squamous epithelial cells are flattened in shape

- many of the cells in epithelium have cilia.

45
Q

What are palisade cells?

A

closely-packed photosynthetic cells within leaves

46
Q

How are palisade cells well adapted to their function?

A
  • long and cylindrical, so they can pack together quite closely but with a little space between them for air to circulate; carbon dioxide in these air spaces diffuses into the cells
  • large vacuole so that the chloroplasts are positioned nearer to the periphery of the cell, reducing the diffusion distance for carbon dioxide
  • contain many chloroplasts- the organelles that carry out photosynthesis
  • contain cytoskeleton threads and motor proteins to move the chloroplasts- nearer to the upper surface of the leaf when sunlight intensity is low, but further down when it is high
47
Q

What is a guard cell?

A

in leaf epidermis, cells that surround stomata

Biology A-Level -James (18 decks)

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