cell division and specialisation Flashcards
what are the 3 functions of mitosis
- growth of multicellular organisms
- replacement of cells and repair of tissues
- asexual reproduction
what is asexual reproduction
the production of new individuals of a species by a single parent organism – the offspring are genetically identical to the parent
what are some differences between sexual and asexual reproduction
Asexual:
- one parent
- offspring genetically identical
- no fusion of gametes
- faster creates a large number of offspring quickly
Sexual:
- two parents
- offspring are genetically different
- fusion of gametes
- slower creates a small number of offspring
outline what happens in the G1 phase of interphase
- organelles replicate
- transcription + translation occurs
- size of cell increases
what is checked for in the G1 checkpoint
cell has grown correctly
DNA damage
outline what happens during the S phase of interphase
DNA replicates so that the two daughter cells can each get one set of DNA
what is checked for during the G2 checkpoint
checks that DNA has been replicated correctly
outline what happens during the G2 phase of interphase
energy stores used during ‘S’ phase are replaced, cells continue to carry out transcription and translation.
chromosomes are repaired, cell size increases.
what happens if a cell fails a checkpoint
it leaves the cell cycle and enters G0 phase or undergoes apoptosis.
what happens to fully differentiated cells such as neurons
they can enter G0 permenantly.
what other scenario may a cell enter G0 phase, give an example
Cells can enter G0 temporarily until there is a signal to divide, for example B memory cells are triggered to divide when there is an infection.
why can bacteria not undergo mitosis
because mitosis is the division of the nucleus, bacterial cells do not contain a nucleus. In addition bacterial cells do not form a mitotic spindle
outline the stages of mitosis
prophase - chromosomes condense and become visible, nucleolus dissapears and nuclear membrane breaks down. Pairs of centrioles move to each pole. Proteins form spindle fibres which attach to the centromere of each chromosome.
metaphase - spindle apparatus is compeltely formed, chromasomes are lined up at the equator of the cell
M checkpoint: checks that chromasomes are assembled correctly on the mitotic spindle.
anaphase - centromere divides into two, spindle fibres shorten, which pulls the sister chromatids to opposite poles of the cell
telophase - chromatids reach the poles of the cell. Spindle apparatus breaks down, nuclear membrane reforms. Chromosomes uncoil back to their chromatin state. nucleolus reappears
Outline the process of cytokinesis
- central cell membrane is pulled inwards by the cytoskeleton, creates a furrow which gradually deepens
- membranes fuse to form 2 independant cells
what are 2 differences that occur in cell division in plants
- centrioles do not play a role in forming the spindle apparatus
- during cytokinesis cell membrane cannot form a furrow, instead vesicles from the golgi apparatus form membrane structures down the centre of the cell, these fuse together to form a central cell membrane which divides the cytoplasm into 2. A new cellulose cell wall forms down the centre.
how many chromosome pairs/ chromosomes does each body cell have
23 pairs
46 chromosomes
how many chromosomes do gametes have
23
outline how u may set up a microscope to investigate mitosis
squashed slide may be used
- treat the tips of growing roots in HCl
- then spread the cells thinly on a microscope using a mounted needle.
- add stain to make chromosomes visible
- lower cover slip gently ensuring no air bubbles
- place under microscope and set objective lens to lowest magnification
- use coarse adjustment knob to lower lens down
- use fine adjustment knob to re-adjust focus.
how are squamous epithelium tissue specialised for function
single layer of flat cells that line a cell surface, eg alveoli. They provide a thin exchange surface for substances to diffuse aross a short distance quickly
how is ciliated epithelium specialised for function
is a layer of cells covered in cilia. eg found in trachea. Cilia waft mucous down to the digestive system - serves as a primary defence against pathogens
how is cartillage specialised for function
is connective tissue found in joints, formed when chondroplasts secrete extracellular matrix, this cushions joints.
what is the role of meiosis
meiosis is a form of nuclear devision that results in production of haploid cells. produces gametes used in sexual reproduction and introduces genetic variation
what is a homologous pair
two chromosomes that have exactly the same gene (same gene because they occupy the same loci) however contain different alleles (versions of genes)
what are recombinant chromosomes
occurs when maternal and paternal chromosomes have exchanged alleles.
what is the main difference between meisosis 1 and meiosis 2
1 - homologous chromosomes are separated from eachother
2 - sister chromatids are separated from each other
outline the stages of meiosis 1
prophase 1 - chromosomes condense and become visible. Homologous chromasomes link together forming chiasmata, crossing over can occur and alleles are exchanged. Nuclear membrane breaks down. centrioles move to opposite poles
metaphase 1- pairs of homologous chromosomes are lined up at the equator on the spindle apparatus
anaphase 1 - spindle fibres shorten, homologous chromosomes move towards opposite poles, the chiasmata breaks.
telophase 1 - chromosomes reach their respective poles, nuclear membranes reform, chromosomes uncoil back to their chromatin state
cytokinesis - forms 2 haploid cells.
outline the process of meiosis 2
phrophase 2 - chromosomes condense, become visible, spindle fibres develop ect.
metaphase 2 - chromosomes lined up at equator
anaphase 2 - centromere divides on each chromosome, spindle fibres shorten, chromatids are pulled to opposite poles
telophase 2 - nuclear membranes reform + chromosomes uncoil back to chromatin.
cytokinesis occurs.
what is the equation for finding the number of genetically different gametes produced by independant assortment
2 to the power of n
where n is the number of chromasomes.
(this does not consider crossing over, only independant assortment)
what are 3 processes that occur during meisosis that introduces genetic variation
- Crossing over of non-sister chromatids during prophase I of meiosis
- Independent assortment of homologous chromosomes during metaphase I of meiosis
- Random fusion of gametes during fertilisation
how are erythrocytes specialised for function
They are biconcave in shape which increases the surface area over which oxygen can be absorbed.
- no nucleus to allow more room for haemoglobin for maximum oxygen capacity
- cytoplasm countains high amounts of haemoglobin which oxygen binds to
- elastic membrane which allows the cell to be flexible and change shape as it squeezes through narrow capillaries.
what are neutrophils and how are neutrophils adapted for function
Function: destroy pathogens by phagocytosis and the secretion of enzymes
Adaptations:
- very flexible shape that allows them to squeeze through cell junctions in the capillary wall
- Their flexibility also enables them to form pseudopodia (cytoplasmic projections) that engulf microorganisms
- There is a large number of lysosomes present in the cell. These digestive enzymes help to digest and destroy invading cells
-A flexible nuclear membrane further helps the cell to penetrate cell junctions. It is thought that this flexibility is what causes the characteristic lobed nucleus
what is the function of sperm cells and how are they adapted
- to fuse with an egg, initate the development of an embryo
- The head contains a nucleus that contains half the normal number of chromosomes (haploid, no chromosome pairs)
- The acrosome in the head contains digestive enzymes that can break down the outer layer of an egg cell so that the haploid nucleus can enter to fuse with the egg’s nucleus
- packed with mitochondria to release energy (via respiration) for the tail movement
- The tail rotates, propelling the sperm cell forwards and allowing it to move towards the egg
How are root hair cells adapted to their function
- Root hair to increase surface area (SA) so the rate of water uptake by osmosis is greater (can absorb more water and ions than if SA were lower)
- Thinner walls than other plant cells so that water can move through easily (due to shorter diffusion distance)
- Permanent vacuole contains cell sap which is more concentrated than soil water, maintaining a water potential gradient
- Mitochondria for active transport of mineral ions
how are palisade cells adapted to their function
- A large number of chloroplasts (the site of photosynthesis) are present in the cytoplasm to maximise the absorption of light for photosynthesis
- The 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
how are guard cells specialised to their function
- 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. Scientists think that these organelles may play a role in the opening of the stomata
