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A-level Biology > 2.6 Cell Division, Cell Diversity and Organisation > Flashcards

2.6 Cell Division, Cell Diversity and Organisation Flashcards

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1
Q

What are the stages of the Cell cycle?

A

Interphase: G1, S, G2
Mitosis: Prophase, Metaphase, Anaphase, Telophase
Cytokinesis

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2
Q

What happens during interphase?

A

G1: Protein synthesis of organelles, cells increase in mass and size, signal to divide again
S: DNA is replicated
G2: Newly synthesised DNA is checked, organelles grow and divide, increase ATP production

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3
Q

How is the cell cycle regulated?

A

G1 Checkpoint:
- cell size
- nutrients
- growth factors
- DNA damage
S Checkpoint;
- chromosomes are checked to see if they have been replicated
G2 Checkpoint:
- cell size
- DNA replication
- DNA damage
Metaphase Check:
- Whether chromosomes are correctly attached to spindle fibres

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4
Q

What happens in Prophase?

A
  • Chromosomes condense and become visible
  • Chromosomes consist of two identical sister chromatids attached at the centromere
  • Centrosomes move to opposite poles
  • Nucleolus disappears and nuclear membrane breaks down
  • Spindle fibres emerge from centrosomes
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5
Q

What happens in Metaphase?

A
  • Centrosomes reach opposite poles
  • Chromosomes line up along the equator of the cell
  • Spindle fibres attach to the centromeres on each chromosome
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6
Q

What happens in Anaphase?

A
  • Sister chromatids separate at the centromere
  • Spindle fibres contract and shorten
  • Chromatids pulled to poles of the cell
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7
Q

What happens in Telophase?

A
  • Chromosomes arrive at the poles and decondense
  • Nuclear envelope reforms around each set of chromosomes
  • Spindle fibres break down
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8
Q

What happens in cytokinesis?

A
  • Cell membrane and cytoplasm divide
  • Formation of two cells
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9
Q

What is the importance of mitosis?

A
  • Produces two genetically identical daughter cells
  • Repairs damaged tissues
  • Asexual reproduction in organisms
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10
Q

What is the significance of meiosis?

A
  • Genetically different offspring increases genetic diversity which is advantageous for natural selection
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11
Q

What are the stages to meiosis?

A

Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
Cytokinesis 1
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2
Cytokinesis

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12
Q

What happens during prophase 1 of meiosis?

A
  • DNA condenses and becomes chromosomes
  • Each chromosome consists of two sister chromatids
  • The chromosomes are arranged side by side in homologous pairs - a bivalent
  • The chromosomes are close together, so crossing over occurs at the chiasmata
  • Nuclear membrane breaks down
  • Centrosomes migrate to poles of cell
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13
Q

What happens during metaphase 1 of meiosis?

A
  • Bivalents line up along the equator
  • The spindle fibres attach to the centromeres
  • The maternal and paternal chromosomes in each pair position themselves independently of the others; independent assortment
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14
Q

What happens during anaphase 1 of meiosis?

A
  • The homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite ends of the spindle
  • The centromeres do not divide
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15
Q

What happens during telophase 1 of meiosis?

A
  • Chromosomes arrive at opposite poles
  • Spindle fibres start to break down
  • Nuclear envelopes form around the two groups of chromosomes and nucleoli reform
    (some plant cells do not reform the nuclear envelope)
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16
Q

What happens during cytokinesis 1 of meiosis?

A
  • Division of cytoplasm
  • Two haploid cells formed
17
Q

What happens during prophase 2 of meiosis?

A
  • The nuclear envelope breaks down and chromosomes condense
  • A spindle forms at a right angle to the old one
18
Q

What happens during metaphase 2 of meiosis?

A
  • Chromosomes line up in a single file along the equator of the cell
19
Q

What happens during anaphase 2 of meiosis?

A
  • Centromeres divide and individual chromatids are pulled to opposite poles
  • This creates four groups of chromosomes that have half the number of chromosomes compared to the original parent cell
20
Q

What happens during telophase 2 of meiosis?

A
  • Nuclear membranes form around each group of chromosomes
21
Q

What happens during cytokinesis 2 of meiosis?

A
  • Cytoplasm divides as new cell surface membranes are formed creating four genetically different haploid cells
22
Q

How are erythrocytes specialised?

A
  • No nucleus - more space for haemoglobin molecules
  • Biconcave shape - increase SA for oxygen absorption
  • Elastic membrane - cell is flexible and can squeeze through narrow capillaries
23
Q

How are neutrophils specialised?

A
  • Multilobed nucleus allows cell to squeeze into small spaces
  • Large number of lysosomes to digest and destroy pathogens
24
Q

How are sperm cells specialised?

A
  • Tail - rotates and propels sperm towards egg
  • Acrosome - digestive enzymes in head - breaks down outer layer of egg cell
  • Many mitochondria - energy for tail movement
25
Q

How are Root hair cells specialised?

A
  • Root hair to increase surface area - rate of water uptake by osmosis is greater
  • Thin walls - water can move through easily (due to shorter diffusion distance)
  • Permanent vacuole - cell sap which is more concentrated than soil water, maintaining a water potential gradient
  • Mitochondria for active transport of mineral ions
26
Q

How are squamous epithelial cells specialised?

A
  • cilia (hair-like structures), which beat in a coordinated way to shift material along the surface of the epithelium tissue
  • Goblet cells secrete mucus which helps to trap dust, dirt and microorganisms - preventing them from entering vital organs
27
Q

How are ciliated epithelial cells specialised?

A
  • a single layer of flattened cells on a basement membrane
  • The layer of cells forms a thin cross-section which reduces the distance that substances have to move to pass through - it shortens the diffusion pathway
  • It is permeable, allowing for the easy diffusion of gases
28
Q

How are guard cells specialised?

A
  • Inner cell walls are thicker (those facing the air outside the leaf) while the outer cell walls are thinner (those facing adjacent epidermal cells). The difference in the thickness of the cell walls allows the cell to bend when turgid
  • The cytoplasm has a high density of chloroplasts and mitochondria.
29
Q

How are palisade cells specialised?

A
  • lots of chloroplasts in cytoplasm - maximise light absorption for photosynthesis
  • Tall and thin shape of the cells allows light to penetrate deeper before encountering another cell wall (cell walls absorb/reflect light) and for many cells to be densely packed together
30
Q

What are the features of stem cells?

A
  1. can divide an unlimited number of times
  2. can remain a stem cell or become specialised
  3. undifferentiated cells
  4. ability to specialise is called potency
31
Q

What are the types of potency?

A
  1. Totipotent: cells can differentiate into any type of cell
  2. Pluripotent: embryonic stem cells that can differentiate into any cell type found in an embryo
  3. Multipotent: adult stem cells that have lost some of the potency associated with embryonic stem cells
32
Q

What are stem cells found in bone marrow and what can they specialise into?

A

multipotent adult stem cells – they can only differentiate into blood cells (red blood cells, monocytes, neutrophils and lymphocytes)

33
Q

Where are stem cells found in plants?

A

The cambium

34
Q

What is the cambium?

A

The cambium is a meristem, which is the term given to any undifferentiated tissue in a plant that has the ability to give rise to new cells

35
Q

How are xylem cells produced from stem cells in plants?

A

the stem cells at the inner edge of the cambium differentiate into xylem cells:
- lose their cytoplasm,
- deposit lignin in their cell walls
- lose their end cell walls

36
Q

How are phloem cells produced from stem cells in plants?

A

the stem cells at the outer edge of the cambium differentiate into phloem cells:
- lose some of their cytoplasm and organelles,
- develop sieve plates

37
Q

How do stem cells differentiate?

A
38
Q

Why is the use of embryonic stem cells banned?

A
  • They have the potential to become human - ethical objections
39
Q

What are the uses of stem cells in medicine?

A
  1. the repair of damaged tissues
  2. treatment of neurological conditions
  3. research into developmental biology

A-level Biology (16 decks)

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