cell division, cell diversity and cell differentiation 2.6 Flashcards
what are the two phases of the cell cycle?
-the M phase and interphase
describe what happens at the G1 phase?
preparation for DNA replication. MRNA’s and proteins required are synthesised (transcription/ translation) =protein synthesis
-growth of cells
- growth of organelles
- increase in number of organellles
what happens at the S phase
- DNA replication
-sister chromatids are produced
-must occur so that the daughters cells have identical DNA
what happens at the G2 phase?
-growth of organelles
-increase in number of organelles
-protein synthesis
-spindle fibres begin to form
what two stages are in the mitotic stage?
- mitosis
-cytokinesis
what is the difference between mitosis and cytokinesis?
-in mitosis the chromosomes separate into two nuclei and in cytokinesis the cell divides into two
what are the reasons for cells entering the G0 phases?
- they are fully differentiated
-repair the DNA
how do we know the cell is in interphase by looking into a microscope?
- the chromosomes are not visible so a dark material called chromatin is seen
What is the difference in the M phase of a plant cell ?
- plants cells don’t have centrioles so they do not play a role in the forming the spindle apparatus
describe what happens in prophase of mitosis
- chromosomes condenses and becomes visible
- nuclear envelope break down
describe what happens in anaphase of mitosis
- sister chromatids are pulled to opposite poles of the cell by the spindle fibres contrcting
- centromere breaks
describe what happens in metaphase of mitosis
-chromosomes line up along the equator of the cell
-spindle fibres attach on the centromere on the chromosomes
describe what happens at telophase in mitosis
-Nuclear envelope begins to form;
-Chromosomes uncoil;
-spindle fibres breaks down
How is the cell cycle regulation?
after each process there are checkpoints to ensure there is no damage
During G1 phase – chromosomes are checked for damage. If damage is detected then the cell does not advance into the S phase until repairs have been made
During S phase – chromosomes are checked to ensure they have been replicated. If all the chromosomes haven’t been successfully replicated then the cell cycle stops
During G2 phase – check for a mutation in the DNA,Daugther cells might not receive identical genetic information
During metaphase – the final check determines whether the chromosomes are correctly attached to the spindle fibres
What is the significance of mitosis in life cycles
-asexual reproduction
-repair of damage tissue/cells
-growth of an organism
in plants,animal and fungi
describe the stages in meiosis 1
- prophase 1- chromosomes condense and become visible
- homologous chromosomes link together forming chiasmata (bivalent)
- crossing-over
- nuclear membrane breaks down
- spindle fibres start to form
metaphase 1 -Bivalents line up on equator of cell
-Independent assortment
anaphase 1-homologous pairs are separated by the spindle fibre and pulled to opposite poles.
- chiasmata between homologous chromosomes but the centromeres are still attached so they are no longer bivalent
telophase 1
- nuclear membrane reforms
- chromosomes uncoil
describe the stages in meiosis 2
- same processes as in one however instead of bivalent chromosomes they just normal( similar to mitosis)
-crossing over also does not take place in prophase two as there are no bivalent pairs
-independent assortment occurs in metaphase 2
why is meiosis known as reduction division?
- because the chromosomes number halves
ways in which variation takes place in meiosis
- crossing over- pairs of chromatids are broken off and exchanged between homologous chromosomes. which exchange alleles (recombinant chromosomes)
- independent assortment- arrangement of homologous chromosomes along the spindle apparatus
- random fusion of gametes - random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a unique combination of alleles
the significance of meiosis in life cycles
- increases genetic variation
- production of haploid cells
erythrocyte’s (red blood cells)
-They are biconcave in shape which increases the surface area over which oxygen can be absorbed
-The cytoplasm contains high amounts of the pigment haemoglobin which can readily bind to oxygen
-No nucleus is present which makes more space inside the cell for haemoglobin molecules for maximum oxygen-carrying capacity
neutrophils
- They are flexible which enables them to engulf microorganisms
- There is a large number of lysosomes present in the cell. These digestive enzymes help to digest and destroy invading cells
-they have a lobed nucleus
spermatozoa (sperm cells)
-many mitrochondria to provide energy for movement
-acrosomes which contain digestive enzymes that allow the sperm cell to penetrate the surface of the egg cell
-flagellum for movement
palisade cells
Adaptations:
- A large number of chloroplasts (the site of photosynthesis) are present in the cytoplasm to maximise the absorption of photons for photosynthesis
-thin allow light to penatrate through
guard cells
- Function: control the opening of the stomata to regulate water loss and gas exchange
- become turgid and flaccid
tissue
Tissues are the same type of cell working together for the same function
root hair cell
-increased surface are to volume ratio for uptake of water and minerals
-thin walls to allow effecient exchange
organs
a group of differnt tissues working for the same function
organ system
- made up of organs
what are stem cells
-undifferentiated cells that can differentiate into any cell type by mitosis
totipotent stem cellls
-can differntiate into any tpe of body cell and also extra-embryonic cells
-early embroyonic cells
pluripotent stem cells
-can differntiate into any type of bosy cells but can not form extra-embryonic cells
-embroyonic stem cells
multipotent stem cells
- can only diferentiate into some body cells
- adult stem cells found in bone marrow
potential uses of stem cells
-to treat alziemers and parkminsons
Squamous epithelial cell
-very thin to provide a short diffusion distance for gases
