Cell division and cellular organisation

Question 1

describe what happens at each stage of the cell cycle

Answer 1

GAP PHASE 1- cell grows, new organelles and proteins are made
G1 CHECKPOINT- the cell checks that the chemicals needed for replication are present and for any damage to the DNA before entering s phase
SYNTHESIS- cell replicates DNA, ready to divide by mitosis
GAP PHASE 2- cell keeps growing and proteins needed for cell division are made
G2 CHECKPOINT- without any damage the cell can enter mitosis
M PHASE- mitosis and cytokinesis followed by metaphase checkpoint

Question 2

what is the structure of chromosomes in mitosis?

Answer 2

beginning: two strands joined in centre by centromere
the separate strands are called chromatids
Interphase until end: two strands on the same chromosome are called sister chromatids
end:when mitosis is over chromatids ends up as one strand chromosome

Question 3

describe each stage of mitosis (PMAT)

Answer 3

INTERPHASE- cell is preparing to divide
DNA replicates
cell growth
ATP production is increased
PROPHASE- chromosomes condense and become visible
nuclear envelope breakdown
nucleolus breaks up and disappears
centrioles migrate to opposite poles
mitotic spindle fibres start to form
METAPHASE- spindle fibres attach onto the centromeres
chromosomes are organised across the centre of cell (metaphase plate)
ANAPHASE- spindle fibres contract and pull the sister chromatids apart
cell starts to elongate
TELOPHASE- the chromosomes are no longer visible
nuclear envelope and nucleolus reformes

Question 4

what happens during cytokinesis?

Answer 4

cytoplasm divides
in animal cell: cleavage furrow forms to divide the cell membrane
in plant cell: the vesicles start to grow until it splits the cell into two
two daughter cells that are genetically identical to original cell
cytokinesis begins in anaphase & ends in telophase

Question 5

what is meiosis and where does it take place?

Answer 5

allows the production of genetically distinct haploid daughter cells from a diploid parent cell
it occurs in the gametes where two haploid gametes fuse to form one diploid cell

Question 6

how is meiosis different to mitosis?

Answer 6

mitosis results in 2 identical daughter cells, whereas meiosis results in 4 sex cells

Question 7

define diploid

Answer 7

a cell containing two complete sets of chromosomes, one from each parent

Question 8

define haploid

Answer 8

quality of a cell organism having a single set of chromosomes
organisms that reproduce asexually are haploid

Question 9

define allele

Answer 9

alternative forms of a gene that arise by mutation and are found at the same place on a chromosome

Question 10

define homologous chromosome

Answer 10

made up of chromosome pairs of approximately the same length, centromere position and staining pattern for genes with the same corresponding loci

Question 11

define chromatid

Answer 11

one-half of a duplicated chromosome

Question 12

define sister chromatids

Answer 12

identical copies of the same chromosome formed by DNA replication
attached to each other by a centromere

Question 13

describe each stage of meiosis

Answer 13

PROPHASE 1- chromosomes condense
begin to pair up
nuclear envelope breakdown
centrioles move to opposite poles
crossing over occurs
METAPHASE 1- pairs of homologous chromosomes line up at the centre
independent assortment occurs
ANAPHASE 1- spindle fibres contract and homologous chromosomes are pulled apart
TELOPHASE 1- nuclear envelope reforms
CYTOKINESIS- two haploid cells are produced
METAPHASE 2- chromosomes line up across the centre
more independent assortment
ANAPHASE 2- spindle fibres contract
sister chromatids pull apart
centromeres splits
TELOPHASE 2- nuclear envelope reforms
CYTOKINESIS- four haploid daughter cells are produced

Question 14

name three things in meiosis that leads to increased variation

Answer 14

recombination of parental genes when haploid cells fuse during fertilisation
independent assortment of chromosomes during metaphase 1&2
crossing over occurs during meiosis 1 resulting in chromosomes containing a different combination of alleles

Question 15

what is a tissue?

Answer 15

a group of cells that are specialised to work together to carry out a particular function

Question 16

what is a muscle tissue?

Answer 16

it's made up of bundles of elongated cells called muscle fibres 
3 different types:
smooth muscle- lining the stomach
cardiac- the heart
skeletal-used to move

Question 17

what is cartilage?

Answer 17

type of connective tissue found in joints
shapes and supports ears, nose and windpipe
formed when cells called chondroblasts secrete an extracellular matrix containing protein fibres which they become trapped inside

Question 18

what is xylem tissue?

Answer 18

plant tissue with 2 jobs- transports water around the plant and supports the plant
contains a hollow xylem vessel cell (which are dead) and living parenchyma cells

Question 19

what is phloem tissue?

Answer 19

transports sugars around the plant
arranged in tubes and is made of sieve cells, companion cells and ordinary plant cells
each sieve cell has end walls with holes in them so that can sap moves through
end walls are called sieve plates

Question 20

what are lungs?

Answer 20

animal organ which carry out gas exchange
contain squamous and ciliated epithelium tissue
have elastic connective tissue and vascular tissue

Question 21

what is the leaf?

Answer 21

plant organ which carries out gas exchange and photosynthesis
contains palisade and epidermal tissue to prevent water loss from leaf
xylem and phloem tissue in the veins

Question 22

what is an organ system?

Answer 22

organs work together to form organ system each system has a particular function