| give a brief description of a somatic cell | somatic cells or body cells are diploid and undergo mitosis |
| give a brief description of a gamete | gametes or sex cells are haploid cells that are created when a diploid cell undergoes meiosis forming 4 haploid gametes |
| what form of reproduction is mitosis | asexual reproduction |
| do all somatic cells divide | no, some differentiate becoming specialised and lose their ability to divide |
| what are the four stages of mitosis | prophase, metaphase, anaphase, and telophase – followed by cytokinesis |
| how long overall does mitosis take | around 1 hour |
| what occurs in the first stage of mitosis | the first stage is prophase
→ nuclear division begins (the nucleus begins to split in two) – nuclear membrane dissipates
→ chromosomes condense and become visible – appear as double stranded
→ the nucleolus shrinks (nucleolus produces and forms ribosomes – found in the nucleus)
→ centrioles move to opposite sides of the cell
→ spindle microtubules or fibres form between the two centrioles – spindle fibres are made of contractile proteins |
| what occurs in the second stage of mitosis | metaphase is second and is the longest stage of mitosis (50% of the time)
→ chromosomes are fully condensed and are lined up along equator
→ each chromosome is attached to a spindle fibre and each chromatid is slowly being pulled to each pole with equal forces from each direction |
| what is the nucleolus | nucleolus produces and forms ribosomes – found in the nucleus) |
| what are microtubules | they are contractile proteins |
| what is kinetochore | it is a protein that connect spindle fibres and chromosomes |
| what is the third stage of mitosis | anaphase is the third and shortest phase only lasting a few minutes
→ centromere holding the two chromatid separates – each chromatid (now a single chromosome) begins moving to opposite poles by shortening microtubules (contractile proteins) |
| what occurs in the last stage of mitosis | telophase is the last stage before cytokinesis
→ chromosomes arrive at the two poles and are grouped at each end of the cell
→ revert to extended fibres of chromatin and nuclear membrane forms around each group of chromosomes
→ spindle microtubules disassemble |
| what are the 2 main stages of the cell cycle | interphase and M phase (mitosis and cytokinesis) |
| what are the stages of interphase | interphase is broken in to three stages – gap 1 (G1), synthesis (S) and gap 2 (G2) |
| what happens in the first stage of interphase | G1 is the longest stage and takes around 8-10 hrs
→ in this stage the cell grows and makes proteins and organelles
→ if the cell is big enough at the end of the stage the cell will pass the restriction or check point and continue to the S phase |
| what is Gap 0 or G0 | some cells such as nerve cells and differentiated tissue cells never leave G1 and don’t undergo mitosis – this is known as G0 stage |
| what occurs in the second stage of interphase | S phase is the second one in interphase and takes 6-8 hours
→ DNA is replicated, and centrioles are duplicated
→ it ends when the DNA in the cell has doubles – each chromosome is now made from two sister chromatids
→ chromosomes become visible at the start of M phase (mitosis and cytokinesis)
– evidence for S phase |
| what is the last stage of interphase | G2 is the phase when the cell actively prepares for mitosis and takes 4-6 hours
→ period of high metabolic activity and lots of protein production (for histones and spindle fibres)
→ after the phase ends the cell goes through a second checkpoint to ensure all genetic material is doubled and the cell is big enough to undergo division |
| where are the two checkpoints in the cell cycle and what do they check for | 1. after G1 - if the cell is big enough at the end of the stage the cell will pass the restriction or check point and continue to the S phase
2. after G2 - cell goes through a second checkpoint to ensure all genetic material is doubled and the cell is big enough to undergo division |
| what is cytokinesis | Division of cytoplasm and is the last stage before the cell becomes two and re-starts interphase |
| what is a cleavage furrow | A cleavage furrow appears at the equator of the cell before the cell splits in to two daughter cells |
| what can the daughter cells do after they are created | daughter cells can either grow via cell enlargement, become specialised or continue to divide |
| what are some features dividing plant cells dont have but somatic cells do | most dividing plant cells do not contain asters or centrioles |
| where are new cells formed in the plant body | New cells are formed in specialised areas of the plant body called meristems – plants contain many meristems but there are four types |
| what are the four meristems of a plant | apical meristem, young leaves, axillary meristems, and root meristems |
| where are apical meristems | growing tip or apex of the plant which divides causing the plant to grow |
| what are young leaves | they are a type of meristem and they demonstrate active growth |
| where are axillary meristems | buds of developing leaves or flowers form in the axils of plants (axils are the upward angle between the main stem and a leaf or branch) |
| what are root meristems | they are a place of active growth - growing tips of roots |
| why cant cytokinesis occur in plants | plant cells have a rigid cell wall so cytokinesis cannot constrict the cell membrane |
| what do plant cells do to divide instead of cytokinesis | Due to the rigid cell wall cytokinesis cannot constrict the cell membrane inwards so instead a new cell wall and membrane is grown along the cell plate (centre of the cell) |
| what is the importance of mitosis | Has two main purposes – growth and repair
→ also, important as it maintains the chromosome number of somatic cells
-> Mitosis also is helpful as when a cell becomes too large and the surface area to volume ratio is too low so it has to divide which increase surface area to volume ratio and makes gas exchanged more efficient |
| why is mitosis important for growth | → multicellular organisms are grown from a single fertilised egg which divides increasing cell number
→ during period of growth cell replacement is higher than cell death however as you grow older and stop growing cell replacement occurs at the same stage as cell death |
| why is mitosis important for repair | responsible for the repair and replacement of damaged cells allowing your body to heal from injuries such as broken bones and scrapes
→ some organisms can generate new body parts when they are lost – sea star |
| what are two genes that help control the cell cycle | proto-onco genes
tumour suppressor genes |
| what is the function of protol-onco genes | Proto-oncogenes promote cancer, produce proteins that stimulate cell division, inhibit cell differentiation, and decreases apoptosis -
-> also triggers apoptosis when cells are faulty, dividing too often, tumourous etc |
| what is the function of tumour suppressor genes | they slow down cell division, help repair damaged DNA, and inform cells when they need to activate apoptosis |
| what are tumour suppressor and proto-onco genes | They are two genes that control the cell cycle and they work together to control the cell cycle and when one is damaged or silenced problems tend to arise |
