cell division, cell diversity and cellular organisation

Question 1

what are the 3 main phases of the cell cycle

Answer 1

1- interphase
2- mitosis
3- cytokinesis

Question 2

explain the 3 stages of interphase

Answer 2

G1- cell grows and makes new proteins to replicate organelles
S- where DNA is replicated
G2- when cell continues to grow and replicated DNA is checked for errors

Question 3

explain the 3 checkpoints of the cell cycle

Answer 3

G1 checkpoint- checks cell has chemicals/nutrients needed for replication, if cell is adequate size and if DNA is damaged
G2 checkpoint- checks if DNA has been replicated without any errors
metaphase checkpoint - each chromosome checked if it’s attached to the spindle

Question 4

what is the cell cycle

Answer 4

controlled process of sequenced stages (interphase, mitosis and cytokinesis) to form two, genetically identical haploid daughter cells

Question 5

how is the cell cycle regulated

Answer 5

• the use of checkpoints to check DNA for any errors via enzymes
• if errors occur cell can destroy itself to prevent passing on harmful mutations

Question 6

what are the 4 stages of mitosis

Answer 6

prophase
metaphase
anaphase
telophase

Question 7

explain what happens in prophase

Answer 7

-chromosomes condense into chromatids, wrapping around histone proteins
-2 centrosomes move to opposite poles
-spindle fibres begin to emerge from centrosomes
-nuclear envelope breaks down into smaller vesicles

Question 8

explain what happens in metaphase

Answer 8

-chromatid pairs align themselves on the spindle equator, attaching by the centromere
-nuclear membrane has completely disappeared

Question 9

explain what happens in anaphase

Answer 9

-sister chromatids are pulled apart to opposite poles by shortening of spindle fibres

Question 10

explain what happens in telophase

Answer 10

-chromatids reach poles of cell
-uncoil, become thin chromosomes again (chromatin)
-nuclear membrane reforms and nucleus reappears
-cleavage furrow can form

Question 11

explain what happens in cytogenesis

Answer 11

-furrow forms around equator ( contracting actin )
-cell surface membrane join up and 2 separate genetically identical daughter cells are produced

Question 12

what is meant my haploid and diploid cells

Answer 12

• diploid (2n) contain 2 copies of each chromosome, one from each parent
• haploid (n) only contain one copy of each

Question 13

what is meant by cell arrest

Answer 13

(apoptosis) is controlled cell death, where the cells stop dividing

Question 14

why is mitosis important in life cycles

Answer 14

-growth
-tissue repair
-asexual reproduction inn plants, fungi and animals

Question 15

what is an allele

Answer 15

a different form of a gene coding for a characteristic

Question 16

define a zygote

Answer 16

a fertilised egg

Question 17

what is a bivalent and how is it formed

Answer 17

its when chromosomes come together to their homologous pairs and form a bivalent and chiasmata

Question 18

what is the importance of meiosis in life cycles

Answer 18

-to produce haploid cells
-genetic variation by independent assortment and crossing over

Question 19

define a homologous chromosome

Answer 19

-pair of chromosomes that have the same genes in the same order, but different alleles ( one maternal, one paternal )

Question 20

state the 2 main stages of meiosis

Answer 20

meiosis I ( PMAT + C)
meiosis II ( PMAT + C )

Question 21

what happens in prophase I and metaphase I of meiosis I

Answer 21

PROPHASE I:
-chromatin condense into chromosomes arranged in homologous pairs
-crossing over occurs
-centrioles migrate to opposite poles
-nuclear envelope breaks down as nucleolus disintegrates
METAPHASE I:
-bivalents align at cell equator
-orientation is random ( independent assortment )
-spindle fibres attach to centromere

Question 22

what happens in anaphase I and telophase I of meiosis I

Answer 22

ANAPHASE I:
-homologous pairs separated and pull chromosomes to opposite cell poles via microtubules
TELOPHASE I:
-nuclear membrane forms around each group of chromosomes
-spindle fibres break down

Question 23

describe what happens in cytokinesis of plant cells

Answer 23

-vesicles from Golgi apparatus gather along equator and merge
-forms new cell surface membrane + middle lamella

Question 24

describe what happens in cytokinesis of animal cells

Answer 24

-cell surface membrane pinches inwards creating a cleavage furrow in the middle of the cell which contracts, dividing the cytoplasm in half

Question 25

what happens in prophase II and metaphase II of meiosis II

Answer 25

PROPHASE II: -nuclear envelope breaks down -chromosomes condense -spindle forms at right angle to old one METAPHASE II: -chromosomes line up in a single file along the equator of the spindle

Question 26

what happens in anaphase II and telophase II of meiosis II

Answer 26

ANAPHASE II: -centromeres divide -individual chromatids are pulled to opposite poles of cell TELOPHASE II: -nuclear membrane forms around each group of chromatids

Question 27

what's the difference between cytokinesis at meiosis I and meiosis II

Answer 27

meiosis I- produces two haploid cells meiosis II- produces four haploid cells

Question 28

what are the levels of organisation

Answer 28

organelle - cell - tissue - organ - organ system - organism

Question 29

what are erythrocytes function and how are they specialised

Answer 29

function: transport oxygen around the body and carbon dioxide into lungs -biconcave disc increases surface area for oxygen be absorbed in -cytoplasm contains haemoglobin to bind to oxygen -no nucleus allows more space for haemoglobin -elastic membrane allows flexibility of cell to change shape as it squeezes through narrow capillaries

Question 30

what are neutrophils function and how are they specialised

Answer 30

function: destroy pathogens by phagocytosis and secretion of enzymes -flexible to: -squeeze through cell junctions in capillary walls -form cytoplasmic projections that engulf microorganisms -contain lysosomes with digestive enzymes that help digest and destroy invading cells -flexible nuclear membrane = lobed nucleus to squeeze through capillaries

Question 31

what are sperm cells function and how are they specialised

Answer 31

function: to fuse with an egg, initiate the development of an embryo and pass on father genes -nucleus contains haploid cells -acrosome contains digestive enzymes to break down egg cell membrane -mid piece has lots of mitochondria to release energy for tail movement -tail rotates, propelling sperm cell forward moving it towards egg

Question 32

what are root hair cells function and how are they specialised

Answer 32

function: absorption of water and mineral ions from soil -root hair increases surface area for greater absorption rate -cell sap maintains water potential gradient -thinner wall decreases diffusion distance -mitochondria for active transport of mineral ions

Question 33

what are squamous epithelial cells function and how are they specialised

Answer 33

function: to line organs and form barriers of protection -thin and flat, allowing for diffusion of materials -permeable -tight junctions form a watertight barrier

Question 34

what are ciliated epithelial cells function and how are they specialised

Answer 34

function: to transport particles/fluids over epithelial surface -hair like projections beat in unison for transport -goblet cells secrete mucus to trap dust, dirt and microorganisms, preventing them from entering vital organs where they could cause infections

Question 35

what are palisade cells function and how are they specialised

Answer 35

function: carry out photosynthesis to produce glucose and oxygen -lots of chloroplast to maximum light absorption for photosynthesis -tall and thin to allow light to penetrate deeper and for cells to be packed closely together

Question 36

what are guard cells function and how are they specialised

Answer 36

function: control the opening of stomata to regulate water loss and gas exchange -inner cell walls are thicker to allow cell to bend when turgid -cytoplasm has lots of chloroplast and mitochondria to control opening of cell

Question 37

give 6 examples of tissues

Answer 37

- ciliated epithelial - squamous epithelial - cartilage - muscle - xylem - phloem

Question 38

describe the xylem

Answer 38

-transport water and dissolved ions -via transpiration -no cell ends -made of dead cells -only upwards movement -outer walls strengthened by lignin, supporting plant

Question 39

describe the phloem

Answer 39

-transport dissolved sugars and amino acids -via translocation -cell ends have sieve plates -two way movement -made of living cells supported by companion cells containing mitochondria to release energy

Question 40

where and how are xylem and phloem tissue ( distinct differentiated outcomes ) derived from

Answer 40

-stem cells in the meristem (growing roots and shoots) on plant cells found in the cambium (region between xylem+phloem tissue)

Question 41

where and how are erythrocytes and neutrophils ( distinct differentiated outcomes ) derived from

Answer 41

-arise from a common stem cell in the bone marrow -stem cells in bone marrow are multipotent adult stem cells

Question 42

what are the 2 key functions of stem cells

Answer 42

1- differentiate by mitosis to produce more undifferentiated cells 2- stem cells can differentiate into specialised cells

Question 43

what are the 4 types of stem cells

Answer 43

-totipotent -pluripotent -multipotent -unipotent

Question 44

what is a totipotent stem cell

Answer 44

can differentiate into any cell type and go on to form whole organisms

Question 45

what is a pluripotent stem cell

Answer 45

can differentiate into most cell types, but cannot form whole organisms

Question 46

what is a multipotent stem cell

Answer 46

can only differentiate into a few different cell types

Question 47

what is a unipotent stem cell

Answer 47

can only differentiate into one type of cell

Question 48

describe embryonic stem cells

Answer 48

-found in early stages of embryo development where they can differentiate into cells to form a foetus -in first few cell divisions, cells are totipotent -after about 7 days, cells become pluripotent

Question 49

describe plant stem cells

Answer 49

-found in the meristematic tissue at the tips of roots or shoots of plants -stem cells are pluripotent -meristematic tissue is also found between xylem and phloem cells in an area know as the vascular cambium -these stem cells differentiate into cells of the xylem and phloem

Question 49

describe adult stem cells

Answer 49

-found in some adult tissues where they can replace faulty cells -stem cells are multipotent or unipotent -stem cells in bone marrow replace worn out erythrocytes and neutrophils

Question 50

what are the 3 main uses of stem cells in research and medicine

Answer 50

- repair of damaged tissues - treatment of neurological conditions - research into developmental biology

Question 51

describe how stem cells can be used in medicine to repair damaged tissues

Answer 51

-tissue damage can occur due to accidental damage, degenerative or autoimmune disease -stem cells can be encouraged to differentiate into a damaged cell type and used to repair damaged tissue, eg *skin cells to treat burn patients *pancreas cells to treat type 1 diabetes

Question 52

describe how stem cells can be used in medicine to treat neurological conditions

Answer 52

-brain cells and neurones can be effected by some diseases, affecting bodies ability to coordinate responses to stimuli -stem cells can be used to generate new neurones in order to treat the symptoms of these conditions, eg *replacing damaged brain cells in Alzheimers and Parkinson's disease

Question 53

describe how stem cells can be used in research into developmental biology

Answer 53

-embyronic stem cells have the ability to differentiate into embryos, allowing scientists to study the developmental