A Level Biology > Cell Division > Flashcards

Cell Division Flashcards

(47 cards)

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1
Q

Cell cycle

A

G1
S
G2
Mitosis
Cytokinesis

{G1, S, G2 are interphase}

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2
Q

Gap 1

A
  • protein synthesis and replication of organelles
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3
Q

S phase

A
  • DNA synthesis — DNA is replicated
  • 2 sister chromatids are held together by centromere
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4
Q

Gap 2

A
  • copied DNA is checked by proof reading enzymes
  • if genes aren’t copied correctly, mutations will occur — new cells won’t work
  • organelle replication
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5
Q

What is chromatin made up of

A

DNA + histones

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6
Q

Mitosis

A

The process or nuclear division where 2 genetically identical nucleus are formed from one parent cell nucleus

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7
Q

Why is mitosis important

A
  • asexual reproduction
  • single celled organisms divide to produce 2 daughter cells that are separate organisms
  • some multicellular organisms produce offspring from parts of the parent
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8
Q

Do bacteria carry out mitosis?

A

NO
- they have no linear chromosomes, spindles or centrioles

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9
Q

Prophase

A
  • chromosomes supercoil to shorten and thicken in prophase (condense)
  • the nuclear envelope breaks down
  • centriole divides in 2 and each daughter centriole goes to pole of cell
  • spindle fibres begin to form
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10
Q

Metaphase

A
  • chromosomes line up along equator of the cell
  • spindle fibres attach to the centromeres of the chromosome
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11
Q

Anaphase

A
  • the centromere breaks - this separates the sister chromatids
  • spindle fibres shorten and pull the chromosomes apart the the poles of the cell
  • Each chromatid is identical to the original chromosome in the parent cell it was copied from
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12
Q

Telophase

A
  • new nuclear envelope forms around 2 sets of chromosomes
  • spindle fibres break down
  • supercoiled chromosomes uncoil into chromatin
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13
Q

Cytokinesis

A

Mitosis is finished
- cytokinesis occurs and the cytoplasm cleaves to finally produce 2 new genetically identical daughter cells (both identical to parent cell)
- this means daughter cell can do same things the parent cell could do

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14
Q

Differences between animal and plant cell cycles

A

Animal cells
- most cells will undergo mitosis and cytokinesis
- cytokinesis starts from outside and goes in

Plant cell
- only special cells called meristem cells can divide
- plant cells do not have centrioles
- cytokinesis starts with the formation of a cell plate where the equator was- the new plasma membrane and new cell wall material is then laid down along the cell plate

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15
Q

Cytokinesis in animals, plants & fungi

A

animals- nip in along ‘cleavage furrow’
plants- along cell plate
yeast (fungi)- budding. Cell undergoes mitosis, then the cell bulges in one side, the new nucleus moves into bulge and the bulge pinched off into a new cell

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16
Q

Meiosis

A
  • 4 daughter cells (haploid)
  • genetically different
  • start from diploid cells (ovaries & testes)
  • gametes
  • 2 divisions
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17
Q

Homologous chromosomes

A

Although they have the same gene, they may contain different alleles from the genes
- because one chromosome is from mum and one from dad

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18
Q

Prophase 1

A
  • chromatin condenses and each chromosome supercoils
  • nuclear envelope breaks down and spindle fibres form
  • chromosomes arranged in homologous pairs (each have 2 chromatids)
  • crossing over occurs where non sister chromatids wrap around each other and may swap sections so that alleles are shuffled
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19
Q

Metaphase 1

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A
  • pair of homologous chromosomes still in cross over state attach along the equator of the spindles
  • each attach to the spindle by centromere
  • pairs are randomly arranged- independent assortment
  • the way they line up here determines how they will separate independently in anaphase
20
Q

Anaphase 1

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A
  • chromosomes pulled apart by spindle fibres
  • centromeres do not divide, each chromosome consists of 2 chromatids
  • crossed over areas separate from each other, resulting in swapped areas of chromosomes and allele shuffling
21
Q

Telophase 1

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A
  • 2 new nuclear envelopes form around each set of chromosomes, cell divides by cytokinesis
  • short interphase where chromosomes uncoil
  • each new nucleus contains half the original no. of chromosomes, but each chromosome consists of 2 chromatids

in most plant cells, the cell goes straight from anaphase 1 to prophase 2

22
Q

Prophase 2

Study These Flashcards
A
  • nuclear envelope breaks down
  • chromosomes coil and condense
  • chromatids no longer identical due to crossing over in prophase 1
  • spindle fibres form
23
Q

Metaphase 2

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A
  • chromosomes attach by their centromere to the equator of the spindle
  • chromatids randomly arranged
24
Q

Anaphase 2

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A
  • centromeres divide
  • chromatids are pulled apart by spindle fibres towards poles
  • chromatids randomly separated
25
Telophase 2
- nuclear envelopes form around each if the 4 haploid cells - *in plants, a tetras of 4 haploid cells is formed*
26
How meiosis produces genetic variation
• Crossing over during prophase 1 shuffles alleles • Independent assortment of chromosomes in anaphase 1 leads to random distribution of chromosomes • 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 from another organism of the same species
27
Specialised cell
A cell that has become differentiated to carry out a particular function E.g. RBC, root hair cell
28
Unspecialised cell
Stem cells. Can develop into different types of cells - embryonic stem cells- can develop into any type of cell - adult stem cell- can replenish cells when needed
29
Hierarchy of stem cells
1. Totipotent 2. Pluripotent 3. Multipotent
30
When stem cells have differentiated into the type of cell they will remain as, they are known as: _\_\_\_\_
Terminally differentiated
31
Erythrocytes
**Function**: carry O2 round the body (from lungs) **Specialisation**: biconcave shape so there is a larger SA to carry oxygen No nucleus to increase space for O2 Flexible to fit through capillaries
32
Neutrophils
**Function**: destroy pathogens in the body **Specialisation**: metabolic adaptations to enable them to function at low oxygen Lobed nucleus Granular cytoplasm contains many lysosomes containing enzymes to attack pathogens
33
Squamous epithelial cells
**Function**: lines areas where diffusion takes place (alveoli and capillaries) **Specialisation**: form smooth thin layer of cells in the tissue Ideal for reducing friction Adapted to be good at diffusion as short diffusion path
34
Ciliated epithelial cells
**Function**: provides the propelling force for transport of substances **Specialisation**: hair like structures (cilia), cilia are long and thin hairs to help increase surface area to project into the airways
35
Sperm cell
**Function**: fertilise egg **Specialisation**: flagella for movement, acrosome contains digestive enzymes to break through hard outer layer, mitochondria, haploid nucleus
36
Palisade cell
**Function**: site of photosynthesis **Specialisation**: lots of chloroplast, long and thin to increase SA, thin cell walls for diffusion of gases
37
Root hair cell
**Function**: absorb water from soil by osmosis **Specialisation**: large surface area and covered in hair like projections, no chloroplast, large vacuole
38
Guard cell
**Function**: regulate opening and closing of stomata **Specialisation**: strong and elastic, large vacuoles
39
Roles of mitosis
- asexual reproduction - growth & repair
40
What is the xylem tissue made up of
- Xylem vessels - parenchyma cells and fibres
41
How is the xylem formed
Meristem cells produce small cells which elongate and become lignified which kills the cell contents. The ends break down and become long tubes
42
Lignin
- Allows adhesion - stops collapse and helps support - waterproof - lack of end walls (continuous) = allows continuous column of water
43
What is phloem tissue made of
- sieve tubes - companion cells
44
How is the phloem formed
Meristem tissue produces cells that elongate and line in end to end to form a long tube. The ends do not break down completely but form sieve plates between cells. They allow the movement of sugars (sucrose) up and down the tubes
45
Animal tissue is grouped into 4 categories:
1. Connective tissue- hold structures together and provide support 2. Muscle tissue- contract to bring about movement 3. Nervous tissue- convert stimuli and carry electrical impulses 4. Epithelial tissue- layers and lining (squamous epithelial and ciliated epithelial)
46
Squamous epithelial tissue
- made of flattened cells held in place by a basement membrane (collagen + glycoproteins) which attaches the epithelial cells to connective tissue - they are smooth and very thin and flat. This makes them perfect for lining tubes - also found in alveoli walls- short diffusion pathway
47
Ciliated epithelial cells
Found in the lumen of: airways- trachea, bronchi and bronchioles, and fallopian tubes and uterus • goblet cells secrete mucus which catches particles and microbes - the cilia waft it up to the throat to be swallowed • Cilia waft egg cells from the ovary along the Fallopian tube • Cilia move in a synchronised rhythmic wave
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