2.1.6-Cell Division,Diversity and Organisation Flashcards
what are the 5 stages of the cell cycle?
- growth 1
- synthesis
- growth 2
- mitosis
- cytokinesis
what 3 parts of the cell cycle are known as interphase?
interphase= growth1, synthesis, growth 2
what happens in growth 1?
cellular contents are duplicated, cell growth, metabolic rates, increased number of organelles
what happens in growth 2?
cell ‘double checks’ duplicated chromosomes for error, making repairs if needed, cell growth and preparation for division
what happens in both growth 1 and 2?
protein synthesis
what happens during synthesis of the cell cycle?
- dna replication
- each chromosome becomes two genetically identical copies.
what percentage of the cell cycle is interphase?
95%
how is the cell cycle regulated?
- with checkpoints, G1, G2, M checkpoint
- G1- ready to divide?
- G2-hows dna?
- M= hows chromosomal alignment
what do checkpoints within the cell cycle ensure?
they ensure that the cell progresses through different stages of the cycle at appropriate times.
what are the 3 reasons for cells to enter G0 (cell arrest) stage of the cell cycle?
- cell is differentiated
- dna damage, leads to cancer
- senescent cells, reached high number of divisions
what is mitosis?
a form of cell division that produces identical cells that contain identical genetic dna.
what are the 4 stages of mitosis?
- prophase
- metaphase
- anaphase
- telophase
what occurs during prophase of mitosis?
- nuclear envelope breaks down and subsequently disappears
- chromosomes condense, and centrioles move to opposite poles
- spindle fibres form
what happens during metaphase of mitosis?
- chromosomes move to equator and attach to spindle fibres via centromeres
- can align in centre as nucleus is no longer there
what happens during anaphase of mitosis?
- sister chromatids are separated and move to opposite poles
- centromeres divide
what happens during telophase of mitosis?
- nuclear envelope reforms
- spindle is broken down/disappears
- chromosomes uncoil/decondense
- start to split into two daughter cells, not completely
what is the significance of mitosis in animal cells?
- enables growth
- body plan
- tissue repair
what is the significance of mitosis in plant cells?
- enables growth
- body plan
- tissue repair
- asexual reproduction
what occurs during cytokinesis of the cell cycle?
-cytoplasm divides completely forming 2 genetically identical cells
in animal cells, how does cytokinesis occur?
a ‘cleavage furrow’ forms and separates the daughter cells
in plant cells, how does cytokinesis occur?
a ‘cell plate’ (the precursor to a new cell wall) forms at the site of the metaphase plate. Once the cell plate reaches the cell walls of the parent cell, new cell walls are produced, separating the new daughter cells
what is meiosis?
a form of nuclear division that results in the production of haploid cells from diploid cells, producing 4 genetically different gametes
what is the significance of meiosis in life cycles?
- increases the genetic diversity of gametes
- genetically different offspring is advantageous for natural selection
how many divisions of meiosis is there?
2
- meiosis1
- meiosis 2
within each division, what are the 4 stages?
- prophase
- metaphase
- anaphase
- telophase
what occurs in prophase 1 of meiosis?
- dna condenses, chromosomes visible
- chromosomes pair up bivalents
- crossing over occurs at chiasma with non-sister chromtids
- nuclear envelope breaks down
- centrioles migrate to opposite, spindle is formed
what occurs in metaphase 1 of meiosis?
- bivalents line up in centre of spindle
- independent assortment occurs with maternal and paternal chromosomes
what occurs in anaphase 1 of meiosis?
- the homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite ends of the spindle, chromatids stay together
- chiasmata= ‘sister’ chromatids that were entangled break off and rejoin
- he centromeres do not divide
what occurs in telophase 1 of meiosis?
- the chromosomes arrive at opposite poles
- spindle fibres start to break down
- nuclear envelopes form around the two groups of chromosomes and nucleoli reform
what occurs in cytokinesis of meiosis 1?
- cytoplasm divides
- cell organelles also get distributed between the two developing cells
- product= two haploid cells
what occurs in prophase 2?
- the nuclear envelope breaks down and chromosomes condense
- a spindle forms at a right angle to the old one
what occurs in metaphase 2?
-chromosomes line up in a single file along the equator of the spindle
what occurs in anaphase 2?
- centromeres divide and individual chromatids are pulled to opposite poles
- this creates four groups of chromosomes that have half the number of chromosomes compared to the original parent cell
what occurs in telophase 2?
-nuclear membranes form around each group of chromosomes
what occurs in cytokinesis of meiosis 2?
- cytoplasm divides as new surface mebrane are formed
- 4 haploid cells form, all being gentically different
how does cytokinesis occur in meiosis 1 in animals?
the cell surface membrane pinches inwards creating a cleavage furrow in the middle of the cell which contracts, dividing the cytoplasm in half
how does cytokinesis occur in meiosis 1 in plants?
- vesicles from the Golgi apparatus gather along the equator of the spindle
- the vesicles merge with each other to form the new cell surface membrane and also secrete a layer of calcium pectate which becomes the middle lamella.
- layers of cellulose are laid upon the middle lamella to form the primary and secondary walls of the cell
what are specialised cells?
cells that have been differentiated and so are specialised to carry out specific functions
what are homolgous chromosomes?
chromosomes in pairs (two chromosomes), of the same size, shape and gene location, containing the same genetic information.
what is a tissue?
made up of a collection of differentiated cells that have specialised function, each tissue has a particular function in the organism
what is an organ?
a collected of adapted tissue that work together to perform a function
what is an organ system?
a group of organs that work together to perform a certain function in an organism’s body
what are the 3 examples of specialised animal cells?
- erythrocytes (red blood cells)
- neutrophills (white blood cells)
- sperm cells (male gamete)
what is the function of erythrocytes and how are they adapted for this?
Function= transport oxygen in blood around the body
- flattened bioconcave shape, decreasing the SA:V ratio
- no nuclei, increasing amount of space for haemoglobin, which carries oxygen
- cannot divide, and no protein synthesis
- no mitochondria so limited respiration
- flexible, to fit through capillaries
- size= 2 by 7 um
what is the function of neutrophills and how are they adapted?
Function= attack and destroy foreign micro-organisms
- multi-lobed nucleus, making it easier to fit through gaps to get to infection sites
- granula cytoplasm contains lysosomes that contain enzymes used to attack pathogens
- size=10-14 um
what is the function of sperm cells and how are they adapted?
Function= adapted to reach, penetrate and fertilise the ovum
- deliver genetic info to female gamete
- flagellum (tail) helps contain mitochondria to supply energy needed to swim
- acrosome(head) contains digestive enzyme, released to digest protective layers around ovum, allowing the sperm to penetrate, fertilisation
what are the examples of specialised plant cells?
- palisade
- root hair
- guard
what is the function and adaptations of palisade cells?
Function= photosynthesis
- present in mesophyll
- contains chloroplasts to absorb large amounts of light
- rectangle shape, so they can be closely packed and a continuous layer
- thin cell walls, increasing the rate of diffusion of CO2
- large vacuole, to maintain turgor pressure
- length= 25-75 um
what is the function and adaptations of root hair cells?
Function=the uptake of water and nutrients
- located near growing tips of surface of roots
- increased surface area due to long extension
- helps maximise uptake from soil
- length= 20-150 um
what is the function and adaptations of guard cells?
Function= control the opening and closing of the stomata
- pairs of cells on leaf surface
- length= 15-20 um
- form openings to allow CO2 to enter for photosynthesis
- lose water, less swollen
- osmotic forces, water influx
- change shape, close stomata, preventing water loss
- thicker cell wall on one side so that cell doesn’t change shape symmetrically when volume of water changes.
what are the three examples of specialised tissues?
- squamous epithelia
- ciliated epithelia
- cartilage
what are the adaptations of squamous epithelia?
- flat appearance
- very thin, flat cells, thin wall
- forms the lining of the lungs, allows rapid diffusion of oxygen into the blood
- present when rapid diffusion across surface is essential
what are the adaptations of ciliated epithelia?
- hair-like structure called cilia on one surface, move in rhythmic manner
- lines the trachea to help mucus be swept away from lungs
- goblet cells that release mucus
what are the adaptations of cartilage?
- connective tissue in ear, nose, ends of bones
- contains fibres of elastin and collagen
- firm, flexible connective tissue
- chondrocycle cells in extracellular matrix
what are the two tissues found in the meristem (slightly behind) of a plant?
- xylem
- ploem
what is a stem cell?
a cell that can divide (by mitosis) an unlimited number of times.
when a stem cell divides, what two things can it become?
- remain a stem cell
- develop into a specialised cell by differentiation
what is potency?
the ability of stem cells to differentiate into more specialised cell types
what are the 3 types of potency and their meanings?
- TOTIPOTENCY= stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells
- PLURIPOTENCY= embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells
- MULTIPOTENCY= adult stem cells that have lost some of the potency associated with embryonic stem cells and are no longer pluripotent, so can only produce a limited range of cell types,in order to help in processes of growth, cell replacement and tissue repair.
where can adult multipotent stem cells be found?
bone marrow.
how do erythrocytes produce from stem cells in bone marrow?
through erythropoiesis
- cell divides into proerythrocytes,changes occur so now cell can only form an erythrocyte
- haemoglobin builds up in cytoplasm, nucleus ejects
- mature erythrocyte is formed.
how does neutrophil produce from stem cells in bone marrow?
- stem cells differentiate, creating changes
- indentations form in the nucleus, giving it a lobed structure
- granules accumulate (these are lysosomes that contain hydrolytic enzymes)
how are xylem and phloem cells produced?
- stem cells at the inner edge of the cambium differentiate into xylem cells, by losing cytoplasm and end cell wall
- stem cells at the outer edge of the cambium differentiate into phloem cells, lose some cytoplasm and organelles, developing sieve plates
