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A-level Biology > Cell Division, Cell Diversity and Cellular Organisation > Flashcards

Cell Division, Cell Diversity and Cellular Organisation Flashcards

1
Q

Cell cycle

A

Before dividing, cells must grow and synthesise new organelles and molecules - these processes occur in a particular order, which is known as the cell cycle

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2
Q

Which part of the cell cycle does the most growth and synthesis occur?

A

Interphase

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3
Q

What percentage of the cell cycle does mitosis typically occupy?

A

5-10%

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4
Q

What happens at G1?

A

First growth phase - organelles are synthesised and bio chemicals are produced

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5
Q

What happens during the S phase?

A

DNA is replicated in the nucleus

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6
Q

What happens during G2?

A

Second growth phase - energy stores are increased and duplicated DNA is checked for errors

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7
Q

What happens during G0?

A
  • Some mature, differentiated cells such as neurones, no longer divide
  • The cycle can be halted in cells with damaged DNA
  • These cells are said to have entered G0
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8
Q

Checkpoints of the cell cycle

A
  • The cycle has checkpoints at the end of G1, S, and G2 that verify whether each phase of the cycle has been completed correctly
  • These checkpoints are controlled by proteins called cyclins and cyclin-dependent kinases
  • The cell cycle can be halted when errors are detected at a checkpoint
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9
Q

The importance of mitosis - processes

A

Growth, repair (of damaged cells), replacement (of cells, such as red blood cells, that have limited lifespans), asexual reproduction (in eukaryotes)

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10
Q

Chromatids

A

Two identical DNA molecules (a chromosome) held together at a centromere)

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11
Q

Prophase in mitosis

A
  • Chromatin (uncondensed DNA in a complex with histones) condenses - chromosomes become visible
  • Nucleolus disappears
  • Centrioles move to the poles of the cell
  • Nuclear envelope breaks down (towards the end of prophase)
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12
Q

Metaphase in mitosis

A
  • Spindle fibres (organised by the centrioles) attach to centromeres (towards the end of prophase/beginning of metaphase)
  • Chromosomes line up along the centre (equator) of the cell
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13
Q

Anaphase in mitosis

A
  • Spindle fibres shorten
  • Centromeres divide
  • Chromatids are separated and pulled to opposite poles of the cells
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14
Q

Telophase in mitosis

A
  • Chromatids are at the poles of the cells (and can be referred to as daughter chromosomes)
  • Nuclear envelopes reform around each set of chromosomes
  • Chromosomes uncoil (and are no longer visible)
  • Cell division (cytokinesis) begins
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15
Q

Cytokinesis

A
  • The division of a cell (cytokinesis) begins in telophase, resulting in two genetically identical cells
  • Each cell receives approximately half of the organelles and cytoplasm from the original cell
  • In animals: a cleavage furrow forms (i.e. cell surface membranes are pulled together by the cytoskeleton)
  • In plants: the cell wall prevents cleavage furrows. The two daughter cells are instead separated by new cell wall production down the centre of the original cell
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16
Q

Meiosis

A

Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells

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17
Q

Prophase I of mitosis

A
  • The key events of mitotic prophase occur (i.e. nuclear envelope disintegrates, nucleolus disappears, spindles form, chromosomes condense)
  • Homologous chromosomes pair up to form bivalents
  • Crossing over occurs
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18
Q

Metaphase I of mitosis

A
  • Homologous pairs (bivalents) line up at the cell equator

- Independent assortment of chromosomes

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19
Q

Anaphase I

A
  • Homologous chromosome pairs are separated (random segregation) - sister chromatids both remain attached to centromeres
20
Q

Telophase I

A
  • Chromosomes assemble at either pole

- Cytokinesis (cell division) - two haploid cells formed

21
Q

Prophase II

A

Chromosomes condense, nuclear envelope breaks down, and spindles form

22
Q

Metaphase II

A
  • Chromosomes line up at equator (as in mitosis)

- Independent assortment of chromatids

23
Q

Anaphase II

A

Random segregation of chromatids

24
Q

Telophase II

A

Chromatids assemble at poles

- Cytokinesis (cell division) - four haploid daughter cells are formed

25
Q

What is crossing over?

A
  • Non-sister chromatids (chromatids from different chromosomes in a homologous pair) interweave (at points called chiasmata) forming bivalents
  • Genetic material is exchanged between homologous chromosomes, produces new combinations of alleles
  • Happens during prophase I
26
Q

Independent assortment of chromosomes

A
  • When homologous chromosomes move to the cell equator, the alignment of each chromosome (i.e. on which side of the cell it is positioned) is random
  • When homologous chromosomes are separated in anaphase I, many different chromosomes combinations can be formed in daughter cells
  • Happens during metaphase I
27
Q

Independent assortment of chromatids

A
  • Chromosomes line up at the cell equator. The side on which each sister chromatid is positioned is random
  • Sister chromatids are no longer identical (due to crossing over), therefore many chromatid combinations are possible in daughter cells
  • Happens during metaphase II
28
Q

Red blood cells/erythrocytes

A
  • Flattened, biconcave shape - increases the SA:V ratio to increase the rate of oxygen diffusion
  • No organelles - more space available for haemoglobin
  • Flexible due to protein arrangements in membranes - ability to squeeze through capillaries
29
Q

Neutrophils

A
  • A type of white blood cell
  • Multi-lobed nucleus - ability to squeeze through gaps in capillary walls to reach infections
  • Many lysosomes - they contain hydrolytic enzymes (to destroy pathogens)
30
Q

Sperm cells

A
  • Flagellum - for movement towards the egg
  • Many mitochondria - to supply energy for movement
  • Acrosome - contains digestive enzymes to enable the sperm to penetrate the egg
31
Q

Palisade cells

A
  • Many chloroplasts (packed close together) - high rate of light absorption for photosynthesis
  • Thin cells walls - greater carbon dioxide diffusion rate
  • Large vacuole - To maintain turgor pressure
32
Q

Root hair cells

A
  • Long, narrow extensions of the cell - large surface area to increase water and mineral uptake from the soil
  • Large vacuole with a high concentration of dissolved solutes - lower water potential to increase rate of water uptake from the soil
33
Q

Guard cells

A

Two kidney-shaped cells with thickened inner cell walls - they control when stomata open (depending on the requirement for gas exchange and water levels in the plant)

34
Q

Squamous epithelium

A
  • Location:
  • Structural features:
  • Function:
35
Q

Ciliated epithelium

A
  • Location: trachea
  • Structural features: cilia on the outside of cells
  • Function: sweep mucus from trachea
36
Q

Cartilage

A
  • Location: joints (between bones)
  • Structural features: firm and flexible
  • Function: protective connective tissue
37
Q

Skeletal muscle

A
  • Location: attached to bones
  • Structural features: contractile proteins
  • Function: movement of the skeleton
38
Q

Xylem

A
  • Location: plant stem
  • Structural features: elongated dead cells strengthened by lignin
  • Function: transport of water
39
Q

Phloem

A
  • Location: plant stem
  • Structural features: perforated walls
  • Function: transport of nutrients
40
Q

Organs

A

Organs are collectives of several tissues that combine to perform a function or range of functions, for example, the heart comprises squamous epithelium, endothelium, and cardiac muscle, as well as other tissues

41
Q

Organ systems

A
  • Organs that work in conjunction with each other

- e.g. digestive system - oesophagus, stomach, liver, pancreas, gall bladder, gastrointestinal tract

42
Q

Organisational hierarchy

A

Specialised cells → tissues → organs → organ systems → whole organism

43
Q

Stem cells

A

Undifferentiated cells with the potential to differentiate into a variety of the specialised cell types of the organism

44
Q

Totipotent (potency of stem cell)

A
  • Which cells can they divide to form? - any (and they have the potential to form a whole organism
  • Examples: the first 16 cells of an animal zygote, plant meristem cells (including cambium tissue, which differentiates into xylem and phloem tissue)
45
Q

Pluripotent (potency of stem cell)

A
  • Which cells can they divide to form? - All tissues (but not a whole organism)
  • Examples: early embryonic cells (in the blastocyst)
46
Q

Multipotent (potency of stem cell)

A
  • Which cells can they divide to form? - a limited range of cells
  • Examples: haematopoietic cells (in bone marrow), which can differentiate to form all blood cells, including erythrocytes and neutrophils
47
Q

Current uses of stem cells:

A
  • Drug testing in vitro (i.e. testing drugs on cultured cells in a laboratory)
  • Studying developmental biology and disease development in vitro
  • Treatment of burns
  • Bone marrow transplants to replace stem cells destroyed during cancer treatment

A-level Biology (32 decks)

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