2.1.6 Cell division and cellular organisation

Question 1

What is the cell cycle?

Answer 1

highly ordered sequence of events that takes place in a cell, resulting in cell division and the formation of 2 genetically identical daughter cells.

Question 2

stages of the cell cycle

Answer 2

-interphase/longest phase, 95% (G1,S,G2)
-mitotic/M phase(mitosis and cytokinesis)

Question 3

What happens during interphase?

Answer 3

-DNA replication and checked for errors, and organelles replicated for spares
-protein synthesis in cytoplasm
-growth and division of chloroplasts in plant/algal cell cytoplasm
-metabolic processes in cells i.e respiration
-increased ATP production(provides energy for cell division)

Question 4

G1 phase(first growth phase)!

Answer 4

(preparing for DNA replication)
-protein synthesis occurs for synthesis of organelles (transcription +translation)
-organelles replicate
-cell grows in size

Question 5

What are the role of checkpoints?

Answer 5

-monitor and verify accurate completion of each cell cycle before cell moves on
-HALTS the cycle if error is found and fixes it or the cell goes through apoptosis(programmed cell death)

Question 6

G1 checkpoint

Answer 6

-checks for chemicals/nutrients needed in replication
-DNA damage
-growth factors and cell size

Question 7

S phase(synthesis)!

Answer 7

-DNA is replicated in the nucleus
-centrioles replicate
-DNA polymerase makes many random and spontaneous errors resulting in DNA mutations

Question 8

types of DNA mutations

Answer 8

beneficial
neutral(occur in introns, or a silent mutation)
harmful

Question 9

G0 phase

Answer 9

(alternative for S phase)
-can be triggered in early G1
-these cells spend all their time in G0do not replicate: may differentiate and become specialised i.e blood cells with no nucleus
OR
have become SENESCENT(have completed the max number of cell divisions) OR
cell may have damaged DNA and can no longer divide

Question 10

G2 phase(2nd growth phase)

Answer 10

-cell continues to increase in size
-ATP production increased through respiration
-protein synthesis for spindle fibres used in mitosis

Question 11

G2 checkpoint

Answer 11

-duplicated DNA is checked for errors(replication AND damage)
-cell size

Question 12

Mitotic phase

Answer 12

-period of cell division:
Mitosis, where the nucleus divides
Cytokinesis, the cytoplasm divides and 2 cells are produced

Question 13

Control of the cell cycle

Question 14

Why are checkpoints important?

Answer 14

to ensure a cell only divides at the right amount of growth, the DNA is error free and chromosomes are correctly positioned during mitosis to ensure 2 genetically identical daughter cells are created from a parent cell

Question 15

Types of checkpoints

Answer 15

-G1
-G2
-Metaphase/spindle assembly= checking that the correct number of chromosomes are present and have attached to spindles and aligned in mitosis

Question 16

Why is mitosis important in life cycles?

Answer 16

all multicellular organisms use this to growth, replacement and repairing of tissues(need genetically identical daughter cells)
-essential for asexual reproduction in plants, animals and fungi (allows for genetically identical offspring)

Question 17

Structure of chromosomes in mitosis

Answer 17

two chromatids joined together in the middle by a centromere(sister chromatids)
-a chromosome contains one DNA molecule(before division, each chromatid has one DNA molecule so every chromosome has 2)
-each chromosome made an identical copy of themselves during interphase

Question 18

What happens to chromatids after mitosis?

Answer 18

they end up as one-strand chromosomes in the new daughter cells

Question 19

Prophase

Answer 19

-chromatin fibres coil and condense to form chromosomes that are visible when stained in a light microscope.
-centrioles migrate to opposite ends of the cell(form a network of protein fibres called the spindle)
-the nuclear envelope breaks down into vesicles and chromosomes lie freely in the cytoplasm.

Question 20

Metaphase

Answer 20

-spindle fibres(what forms the spindle) attach to specific areas on the centromere
-chromosomes are organised by them along the the middle of the cell at the spindle equator
*checkpoint= the cell checks that the correct number of chromosomes are present and have attached to spindles and aligned in mitosis

Question 21

Anaphase

Answer 21

-centromeres divide, separating each pair of sister chromatids
-spindle fibres contract/shorten and the chromatids are pulled to opposite poles
*‘V’-shape chromatids because they are being dragged by centromeres through liquid cytosol.
-requires ATP

Question 22

Telophase

Answer 22

-chromatids reach the opposite poles on the spindle and uncoil and become long again(chromosomes now)
-nuclear envelope forms around each group of chromosomes, spindle fibres break down and 2 nuclei are formed ready for cytokinesis

Question 23

Cytokinesis in animal cells

Answer 23

• the cell membrane pinches inwards and a cleavage furrow forms around the middle of the cell or a contractile ring and divide the cell membrane
  *cell surface membrane is pulled inwards by the cytoplasm until close enough to fuse around the middle to form genetically identical daughter cells.

Question 24

Cytokinesis in plant cells

Answer 24

(no cleavage furrow due to plant cell walls as cellulose cannot break)
-vesicles from Golgi assemble where the metaphase plate was formed and fuse with each other to form the new cell membrane to divide the cell in 2.
-new sections of cell wall form along membrane

Question 25

Why is meiosis significant in life cycles?

Answer 25

-produces haploid cells via a reduction division(diploid to haploid) -cells formed are all genetically different because each new cell ends up with a diff combination of alleles leading to genetic variation -prevents doubling of the chromosome number at fertilisation

Question 26

What is the function of meiosis?

Answer 26

occurs in the ovaries/testes to produce gametes (male is continuously producing gametes whereas a female has a full set of gametes since in the womb)

Question 27

how many chromosomes do somatic(body) cells have?

Answer 27

-46 chromosomes -diploid number of chromosomes(2n): 2 copies of each chromosome, one from each parent

Question 28

Why is meiosis a reduction division?

Answer 28

-each gamete produced contain half of the chromosome number of the parent cell or 1 copy of each chromosome HAPLOID because they have not gone through fertilisation to form a zygote

Question 29

What are homologous chromosomes?

Answer 29

-pairs of matching chromosomes(one from each parent to make up two full sets of genes in the nucleus, a pair of genes for each characteristic) -has the same genes at the same loci but different alleles

Question 30

What are alleles?

Answer 30

-different versions of the same gene(gene variants) -all have the same loci -because chromosomes are homologous, they will be the same size(when visible in prophase) and the centromeres will be in the same positions.

Question 31

How many divisions does meiosis involve?

Answer 31

2

Question 32

What are the maternal and paternal cells called in meiosis?

Answer 32

germ-line cells

Question 33

What is meiosis 1?

Answer 33

the reduction division where the pairs of homologous chromosomes are separated into 2 cells to produce haploid cells

Question 34

Prophase 1

Answer 34

-DNA condense to form visible chromosomes and get shorter and fatter -homologous chromosomes(bivalent) pair up, moving them through the liquid cytoplasm as they are brought together non sister chromatids exchange alleles, point at which the crossing over occurs is called the chiasma. they now have the same genes but diff combo of alleles= crossing over -centrioles move to opposite poles to form spindle fibres -nuclear envelope breaks down

Question 35

What does the point at which the chiasmata form determine?

Answer 35

the amount of genetic variation

Question 36

Metaphase 1

Answer 36

-homologous pairs line up across the centre of the cell and attach to the spindle fibres by their centromeres -INDEPENDENT ASSORTMENT= orientation of hom pairs is independent of others and random(maternal or paternal chromosomes can end up facing either pole)--} results in genetic variation as there are many possible combinations of assortment(2'23)

Question 37

Anaphase 1

Answer 37

-the spindle contracts, microtubules pulling the pairs apart, one chromosome to each end of the cell -the entangled sister chromatids break off and rejoin at the chiasmata(sometimes DNA is exchanged and forms recombinant DNA with diff allele combination leading to genetic variation as sister chromatids are not indentical)

Question 38

Telophase 1

Answer 38

-the chromosomes assemble at each pole + uncoil and a nuclear envelope forms around each group -spindle fibres being to break down -nuclear membrane forms -cytokinesis occurs and two haploid daughter cells are produced

Question 39

What happens during meiosis 2?

Answer 39

the pairs of chromatids present in each daughter cell are separated, forming 4 haploid daughter cells in total

Question 40

Steps of meiosis 2

Answer 40

-prophase= same as mitosis -metaphase= individual chromosomes assemble along spindle equator, no longer identical chromatids so there is independent assortment and more gen variation -anaphase= centromeres divide and chromatids pulled to opposite poles to form 4 haploid daughter cells(inherits 1 chromatid from each chromosome) -telophase= the chromosomes uncoil and form chromatin, nuclear envelope and nucleolus becomes visible, membrane forms around each group -cytokinesis= result in 4 haploid cells due to the reduction division, genetically different due to crossing over and independent assortment

Question 41

When does genetic variation occur?

Answer 41

-in meiosis to make gametes all genetically different -during fertilisation when any egg can fuse with any sperm(random fusion of gametes) as **gametes are not identical** which produces **large number of allele combinations** -mutations as DNA polymerase makes random, spontaneous errors in S phase which **DNA checkpoints did not recognise**(changes DNA sequence)

Question 42

Why is genetic variation important?

Answer 42

new individuals have a new mixture of alleles making them genetically unique

Question 43

How is genetic variation created in gametes?

Answer 43

-crossing over in P1= chromatids will have **new combo of alleles** but amount of variation **depends on distance between crossover points** -independent assortment of hom chromosomes in M1 and chromatids in M2= 4 daughter cells have diff combination of maternal and paternal chromosomes, **large number of allele combinations**

Question 44

What are stem cells?

Answer 44

-undifferentiated cells that are not adapted to any particular function and have the potential to differentiate to develop into different types of specialised cells

Question 45

What are the function of stem cells?

Answer 45

-they undergo cell division again and again* and are the source of new cells necessary for growth, development and tissue repair. *until specialised where they lose ability to divide and enter G0

Question 46

What happens if activity of stem cells is not controlled?

Answer 46

-if they divide too slow, tissue is not effectively replaced leading to ageing -if division is uncontrollable then tumours form which can lead to development of cancer

Question 47

What is a stem cell's potency?

Answer 47

its ability to differentiate into different types of cells. greater number of differentiations= greater potency

Question 48

types of potency

Answer 48

totipotent: can differentiate into any type of cell i.e zygote pluripotent: can form all tissue types but not whole organisms, present in early embryos and are the origin of diff types of tissues in an organism multipotent: can only form a range of cells with a certain type of tissue i.e haematopoietic stem cells in bone marrow can give rise to blood cells

Question 49

What is differentiation?

Answer 49

the process by which a cell becomes specialised for its job(first they divide) (what form this adaptation takes is dependant on the tissue, organ or organ system in which the cell belongs)

Question 50

What are the 2 sources of animal stem cells?

Answer 50

embryonic and tissue(adult)

Question 51

Embryonic stem cells

Answer 51

-present at a very early stage of embryo development and are totipotent -form a blastocyst after around 7 days and enter a pluripotent) state(remain in state inside fetus until birth

Question 52

Tissue(adult) stem cells

Answer 52

-present throughout life from birth -found in specific areas i.e bone marrow -multipotent

Question 53

where are blood cells derived from?

Answer 53

undifferentiated adult stem cells in the bone marrow

Question 54

What blood cells are formed from the adult stem cells?

Answer 54

neutrophils and erythrocytes

Question 55

How are erythrocytes(red blood cells) specialised for their function?

Answer 55

they carry oxygen in the blood -they have a flattened biconcave disc shape to provide a large surface area for gas exchange and transporting oxygen around the body -no nucleus in mammals (DO NOT CONTAIN DNA) so more room for haemoglobin(the protein that carries oxygen) -flexible so they can squeeze through narrow capillaries

Question 56

How are neutrophils(a type of white blood cells) specialised for their function?

Answer 56

defend the body against disease(part of the immune system) -flexible shape due to multi lobed nucleus allows them to engulf foreign particles or pathogens as it easier to squeeze through small gaps to get to site of infection -many lysosomes in their granular cytoplasm contains digestive enzymes to help break down engulfed particles (their production via stem cells in the bone marrow increase during infection)

Question 57

How are epithelial cells specialised for their function?

Answer 57

they cover the surface of organs, cells are joined by interlinking cell membranes and a membrane at their base -ciliated epithelia have cilia that beat to move particles away -other epithelia i.e in the small intestine, have microvilli which folds in the cell membrane to increase the cell's SA -squamous epithelia i.e in the lungs are very thin to allow efficient diffusion of gases

Question 58

How are sperm cells specialised for their function?

Answer 58

male sex cells/gametes that deliver genetic info to the female gamete. -have a flagellum so they can swim to the egg(female sex cell) -have many mitochondria to provide the energy to swim -acrosome on head contains digestive enzymes to enable the sperm to penetrate the surface of the egg by digesting protective layers around ovum

Question 59

What are stem cells in plants used for?

Answer 59

-to make new shoots and roots throughout their lives -can differentiate into various plant tissue

Question 60

Meristematic tissue(meristems)

Answer 60

-stem cells found here are pluripotent -found wherever growth is occurring in plants

Question 61

What happens in the root and stem of a plant?

Answer 61

-stem cells of the vascular cambium divide and differentiate to become xylem vessels and phloem sieve tubes(starts with cambium meristem dividing, then differentiation results in meristem cells sandwiched between phloem and xylem)

Question 62

How are palisade mesophyll cells specialised for their function?

Answer 62

when in leaves, do most of the photosynthesis -contain many chloroplasts so they can absorb a lot of sunlight -walls are thin so CO2 can easily diffuse into cells -cells are rectangular box shaped so they can closely pack together to form continuous layer -large vacuole to maintain turgor pressure(membrane pushing against cell wall)

Question 63

How are root hair cells specialised for their function?

Answer 63

absorb water and mineral ions from the soil near the growing tips on a root -they have a larger SA for absorption -thin, permeable wall for entry of water and ions -cytoplasm contains extra mitochondria to provide the energy needed for active transport

Question 64

How are guard cells specialised for their function?

Answer 64

pairs on the surfaces of leaves to form stomata(small opening), necessary for CO2 to enter plants for photosynthesis -in the light, guard cells take up water into their vacuoles and become turgid and walls force them to bend outwards and open stomata to exchange gases for photosynthesis -when they lose water, they become less swollen due to osmotic forces and change shape to prevent more water loss -thin outer walls and thick inner walls change shape asymmetrically as its volume changes

Question 65

What neurological conditions can be treated with stem cells?

Answer 65

Parkinson's= suffer from uncontrollable tremors caused by loss of a nerve cell in the brain that releases dopamine which is needed to control movement --} stem cells may help regenerate dope-producing cells Alzheimer's= nerve cells in the brain die in increasing numbers resulting in memory loss--} stem cells may help regrow healthy nerve cells

Question 66

How do stem cells help repair damaged tissue?

Answer 66

Heart disease= results in heart tissue becoming damaged and the body becoming unable to replace damaged cells --} looking into developing ways of using stem cells to make replacement heart cells

Question 67

How can stem cells help research into developmental biology?

Answer 67

-with their ability to divide indefinitely and differentiate into almost any cell they can help the study of changes that occur as multicellular organisms grow and develop from a single cell and why things go wrong.

Question 68

Ethical issues with stem cells

Answer 68

-removal of embryo may result in destruction -using excess embryos from IVF despite debate about when life begins -religious and moral obligations, see it as murder -embryo cannot give consent

Question 69

What are tissues?

Answer 69

A group of cells that are specialised to work together to carry out a particular function within an organism (specialised cells of the same type group together in multicellular organisms)

Question 70

What are the 4 main categories of tissues in animals?

Answer 70

nervous tissue- adapted to support transmission of electrical impulses epithelial tissue-adapted to cover internal + external body surfaces muscle tissue- adapted to contract -connective tissue- adapted to either hold other tissue together or act as transport medium

Question 71

Squamous epithelium tissue

Answer 71

-provide a surface covering and are found in many organs/structures in the body i.e alveoli and blood vessels -single layer/thin cross section of flat squamous epithelial cells lining a surface(one cell thick) -provides a thin exchange change surface for substances as it shortens the diffusion pathway -permeable, allowing for easy diffusion of gases

Question 72

What is the function of epithelial cells in the small intestine?

Answer 72

to absorb food

Question 73

Ciliated epithelium

Answer 73

-found on surfaces where substances need to move i.e trachea where it wafts mucus along -made up of ciliated epithelial cells that are lined with cilia on one surface(beat in a coordinated way to shift material along surface of tissue) -have goblet cells that secrete mucus to trap dirt, dust and microorganisms and prevent them from entering vital organs + infecting

Question 74

Muscle tissue

Answer 74

must contract in for movement -made up of bundles of elongated cells called muscle fibres 3 different types of muscles in animals due to adaptations: smooth(lining of stomach), cardiac(heart), and skeletal*(attached to the bone and contain myofibrils which has contractile proteins) and they are different in structure -all muscle cells have layers of protein filaments in them that can slide over each other causing muscle contraction -high density of mitochondria to provide sufficient energy (via respiration) *muscle cells fuse together during development to form multinucleated cells that contract in unison

Question 75

Cartilage

Answer 75

-strong and flexible connective tissue(provides support) found in the joints -contains fibres of elastin and collagen -shapes and supports the ears, nose and windpipe(forms tracheal rings that support trachea and ensure it stays open/flex and move while we breathe) -formed when chondroblasts secrete extracellular matrix(jelly-like containing protein fibres) which they become trapped inside -prevents the ends of bones from rubbing together and causing damage

Question 76

Xylem tissue

Answer 76

-type of vascular plant tissue that transports water and minerals/dissolved ions throughout plants -no top and bottom(end)walls to form continuous hollow tubes/xylem vessels to draw up water via transpiration -dead cells with no organelles/cytoplasm to allow free movement of water -living parenchyma cells(fills in gaps between vessels -outer walls thickened with lignin(more than normal plant cell wall), strengthens tubes and structural supports plant

Question 77

Phloem tissue

Answer 77

vascular plant tissue that transports dissolved sugars, particularly sucrose, and amino acids throughout plant -arranged in tubes and is made up of sieve cells*, companion cells and some ordinary plant cells. *have end walls i.e sieve plates with holes in them so that sap can move easily through them -few sub cell structures to aid flow of materials

Question 78

What is an organ?

Answer 78

collection of tissues adapted to perform a particular function in an organism

Question 79

The lungs

Answer 79

animal organ which carries out gas exchange -contain squamous epithelium tissue in the alveoli and ciliated in the bronchi etc -have elastic connective tissue and vascular tissue(in blood vessels)

Question 80

The leaf

Answer 80

plant organ which carries out gas exchange and photosynthesis -palisade tissue -epidermis tissue(prevents water loss from leaf) -xylem and phloem tissues in the veins

Question 81

What are organ systems?

Answer 81

a number of organs working together to carry out a major function in the body

Question 82

The respiratory system

Answer 82

brings air into the body so O2 can be extracted and CO2 can be expelled -all organs/tissues/cells involved in gas exchange i.e lungs, trachea, larynx, nose, mouth, diaphragm

Question 83

The circulatory system

Answer 83

moves blood around the body to provide an effective transport system for the substance it carries -made up of the organs involved in blood supply i.e heart, arteries, veins, capillaries

Question 84

Investigating mitosis

Answer 84

-stain specimen(with methylene blue, acetic orcein), put it on a microscope slide and examine under microscope -a 'squash' slide is made by treating tips of growing roots in HCl(break down cellulose connections in cell wall) and breaking them open, spreading cells on slide with mounted needle, adding few drops of stain and physically squashing specimen beneath coverslip -chromosomes are visible once stained under light microscope -should be able to recognise, draw and label each stage of the cell cycle/mitosis

Question 85

How do yeast and bacteria divide

Answer 85

-Yeast undergoes budding -Bacteria undergoes binary fission(cell grows, circular DNA and plasmids replicate, new cell wall grows and cytoplasm divides) which is asexual