How long is spent in interphase and mitosis?
Interphase= 91.7%
Mitosis= 8.2%
Name some of the functions of the cell cycle checkpoints
- identify DNA replication errors
- check cell size
- check for DNA damage
- chromosome attachment to spindle fibres
What happens in mitotic interphase?
S phase= DNA replicates, each chromosome consists of a pair of identical sister chromatids, rapid
G2= Chemicals ensure cell is ready for mitosis by stimulating proteins involved in making chromosomes condense + formation of spindles, cells grow
M phase= cell growth stops, nuclear division
G1= cells grow and increase in size, organelles duplicate, biosynthesis, p53 (tumour supressor) gene controls this phase.
Describe the process of mitosis; prophase, metaphase, anaphase, telophase
Prophase
1. Chromatin condenses into chromosomes which are made up of 2 sister chromatids.
2. Nucleolus disappears, nuclear membrane breaks and centrioles move to poles
3. Spindle fibres form from microtubules.
Metaphase
1. Spindle fibres attach to the centromere of the chromosome and are moved to line along the equator with the help of motor proteins
Anaphase
1. Centromeres holding chromatids divide
2. Microtubules pull chromatids apart and contract so the chromatids move to opposite poles.
Telophase
1. Chromatids reach opposite poles and become new chromosomes of daughter cells
2. Microtubules break down, NE reforms and chromosomes uncoil
What is the significance of mitosis?
- Each daughter cell has a full set of chromosomes that are identical to the parent
- No genetic variation
- when tissues are being repaired the new cells must be exact copies
- offspring are clones, inherit advantageous characteristics so will be suited to survive in the same environment
Describe homologous chromosomes
- 1 chromosome from each parent
- chromosomes with the same gene loci in the same sequence
- they pair to form bivalents in prophase 1
Explain meiosis 1; prophase, metaphase, anaphase, telophase
Prophase
- Chromatin condenses, each chromosome supercoils
- NE breaks down, spindle fibres form
- Crossing over occurs where non-sister chromatids wrap around each other and swap sections so alleles are shuffled
Metaphase
- Spindles attach to centromere and pull into the equator
- Pairs are randomly arranged
- Way that they line up will determine the way they separate
Anaphase
- Microtubules shorten so chromosomes go to opposite poles with the help of motor proteins
- each pole has a whole set of haploid chromosomes
- CENTROMERES DO NOT DIVIDE
Telophase
- NE reforms, crossing over causes cells to be non-identical
- New nucleus has half the original number of chromosomes
Explain meisosi 2; prophase, metaphase, anaphase, telophase
Prophase 2
- NE breaks if it previously reformed and new spindles form
- Chromosomes coil and condense
- chromatids are NOT identical due to previous crossing over
Metaphase 2
- Spindles attach to centromeres and are dragged to the equator of the cell, randomly arranged
- Way that they are arranged= way they will segregate
Anaphase 2
- Fibres contract
- chromatids move to opposite poles by motor proteins
- CENTROMERES DIVIDE
- randomly segregated
Telophase 2
- NE reforms
- 4 haploid cells
What are some disadvantages of asexual reproduction?
- No differentiation = may not be suited to environment
- equally vulnerable
- grow very close together so they may compete for resources
What are advantages of asexual reproduction?
- If conditions are beneficial it reproduces quicker without the need of another partner
- conserves favourable characteristics
What are advantages of sexual reproduction?
- genetic variation means that offspring can withstand changes/ have better chance to survive
What are disadvantages of sexual reproduction?
- Long process (gestation period)
- requires 2 partners
What is differentiation?
The process by which the daughters of stem cells become specialised into different cells
Why do multicellular organisms require differentiation?
- Small SA:vol
- every cell is not in contact with external environment, simple diffusion cannot meet needs
- Division of labour= cells specialise in specific functions
- cooperation between cell types for survival of organism
Describe the specialisation and functions of; erythrocytes
- small, 7.5um, large SA:Volume
- Biconcave disc increases surface area
- Flexible with a well developed cytoskeleton allowing them to change shape so they can fit through capillaries
- No nucleus, mitochondria, RER, small cytoplasm to provide space for haemoglobin
Describe the specialisation and functions of; neutrophils
- 50% of white blood cells
- twice the size of erythrocytes
- multilobed nucleus
- Attracted to infection sites by chemotoxins
- Play a role in phagocytosis
Describe the specialisation and functions of; spermatozoa
- Lots of mitochondria for aerobic respiration, ATP provides energy so tail can move
- Small, long and thin so they can move easily
- Enzyme released from acrosome digests the protective covering of the ovum for fertilisation purposes
- head contains haploid male gamete nucleus and little cytoplasm
Describe the specialisation and functions of; epithelial tissues
- Close together to form continuous sheets
- No blood vessels, cells receive nutrients by diffusion from tissue fluid
- Ciliated= have cilia
- Squamous= flattened
Describe the specialisation and functions of; Palisade cells
- present in mesophyll, contains chloroplasts to absorb light
- cells are rectangular, closely packed to form a continuous layer
- thin cell walls to increase the rate of CO2 diffusion
- large vacuole to maintain turgor pressure
Describe the specialisation and functions of; root hair cells
- Present at surfaces of roots near tips
- long extensions called root hair to increase the SA of cell
Describe the specialisation and functions of; guard cells
- pairs of guard cells are found on surfaces of leaves and form small openings called stomata
- necessary for gaseous exchange
- when guard cells lose water and become less swollen they change shape and stoma closes to prevent further water loss
- cell wall of a guard cell is thicker on one side so the cell does not change shape symmetrically
Describe the specialisation and functions of; xylem tissue
- transport of water and minerals
- vessel elements; elongated dead cells
- walls of these cells are strengthened by lignin
Describe the specialisation and functions of; phloem tissue
- transport of organic nutrients (sucrose)
- composed of sieve tube cells separated by perforated walls called sieve plates
What do chondroblasts do?
- Form extracellular matrix and are immature
- after secreting matrix they mature and are less active
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Biological membranes33
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Communicable diseases65
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Biological molecules54
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Nucleic acids33
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Enzymes32
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Exchange surfaces32
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Cell structure30
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Cell organelles22
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Cell division40
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Transport in animals57
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Transport in plants49
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Classification and evolution51
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Biodiversity57
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Homeostasis69
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Ecosystems31
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Plant hormones27
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Hormones67
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Photosynthesis33
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Nerves44
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Nerves- the brain regions6
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Respiration34
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Inheritance38
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Manipulating genomes23
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Cellular control33
