Cell Division and Cellular Organisation

Question 1

Features of Xylem

Answer 1

Primary function: Transport of water and minerals from roots to shoots
Direction of transport: Unidirectional (upwards)
Cell types: Tracheids, vessel elements
Cell wall composition: Lignified
Cell contents: Dead at maturity
Adaptations for function: Thick, lignified walls for support; pits for lateral water movement

Question 2

Features of Phloem

Answer 2

Primary function: Transport of organic compounds (e.g., sucrose) from sources to sinks
Direction of transport: Bidirectional
Cell types: Sieve tube elements, companion cells
Cell wall composition: Non-lignified
Cell contents: Living at maturity
Adaptations for function: Sieve plates for cell-to-cell communication; companion cells for metabolic support

Question 3

Features of meristematic plant tissue

Answer 3

Can differentiate into various cell types, such as xylem and phloem.
Cells are undifferentiated and actively dividing.
Responsible for plant growth and development.
Found in regions of active growth such as root tips and shoot tips.
Found in regions of the plant where growth occurs, such as the apical meristem and lateral meristem.
Contains cells with specialized organelles for rapid cell division.

Question 4

Features of epidermal plant tissue:

Answer 4

Located primarily on the outer surface of plant organs.
Contains specialized cells like guard cells and trichomes.
May contain stomata, which regulate gas exchange and water loss.
Provides a protective barrier against water loss, pathogens, and herbivores.
Cells are often tightly packed to form a continuous barrier.
May be covered by a waxy cuticle, which can vary in thickness depending on the environment.

Question 5

What happens in G1?

Answer 5

First growth phase, production of enzymes and proteins from which organelles are synthesised are produced and organelles replicate

Question 6

What happens in G0?

Answer 6

Cell leaves cycle (temporarily or permenantly) either for differentiation, damaged DNA or cell aging.

Question 7

What is apoptosis?

Answer 7

Programmed cell death

Question 8

What is senescence?

Answer 8

when the cell can no longer divide

Question 9

What happpens at the G1 checkpoint?

Answer 9

Checkpoint at end of G1 phase, checks for cell size, nutrients, geowth, damage, and moves on or enters resting phase in G0

Question 10

What happens in S phase?

Answer 10

Synthesis phase, DNA is replicated in the nucleus

Question 11

What happens in G2?

Answer 11

Second growth phase, cell continues to increase in size, energy stores are increased and duplicated DNA is checked for errors

Question 12

What happens in the G2 checkpoint?

Answer 12

Checks for cell size, DNA replication and DNA damage

Question 13

What happens in mitosis?

Answer 13

Cell divides into two identical daughter cells

Question 14

What happens in the mitosis checkpoint?

Answer 14

Checks chromosome attatchment to spindle

Question 15

What is the order of the cell cycle for mitosis?

Answer 15

G1, (G0), G1 checkpoint, S Phase, G2, G2 checkpoint, mitosis, mitosis checkpoint

Question 16

What is the order of the stages of mitosis?

Answer 16

Late interphase, prophase, metaphase, anaphase, telophase, cytokenesis

Question 17

What happens in late interphase (mitosis)?

Answer 17

S: DNA replicates so each chromosome is made of two chromatids
G2: replication of more cell organelles and rapid protein synthesis
Centrioles replicate

Question 18

What happens in prophase (mitosis)?

Answer 18

Chromosomes become visible as DNA coils/super coils/condenses - each chromosome is made of two chromatids
The nucleolus disappears
Centrioles move apart to opposite sides of the cell
Spindle fibers form from microtubules
Nuclear membrane breaks down

Question 19

What happens in metaphase (mitosis)?

Answer 19

Centrioles reach the poles and the spindle is complete
Microtubules from the spindle become attatched to the centromeres
Chromosomes are moved by spindle finbres to line up along the equator or metaphase plate of the cell, with chromoatids facing opposite poles
Mitotic spindle created

Question 20

What happens in anaphase (mitosis)?

Answer 20

Centromeres holding chromatids divide
Microtubules from the spindle pull the chromatides apart. They move to opposite poles

Question 21

What happens in telophase (mitosis)?

Answer 21

Chromatides reach each pole and become the new chromosomes of the daughter cells
Microtubules making up the spindles break down
Nuclear envelope reforms
Chromosomes uncoil and become long and thin again

Question 22

What happens in cytokinesis (mitosis)?

Answer 22

The cytoplasm and organelles divide between the daughter cells.
The new cell membrane forms between daughter nuclei
The new cells are genetically identical to each other and the original parent cell

Question 23

What phases are chromosomes present in, and what happens in these phases (mitosis)?

Answer 23

S Phase: DNA duplicated. Sister chromatids joined by centromere.
Telophase: Separated sister chromatids, now chromosomes, uncoil. Nuclear membrane formed around complete sets at poles.
Cytokinesis: nuclei partitioned, 2 new daughter cells

Question 24

What phases are chromatids present in, and what happens in these phases (mitosis)?

Answer 24

Late interphase: DNA replicates, chromosome made of 2 chromatids
Prophase: shorten and thicken, DNA condenses/supercoils
Metaphase: pairs attatch to spindle fibres at equator
Anaphase: Split, now chromosomes, V shape
Telophase: at poles

Question 25

What phases is the nuclear envelope present in, and what happens in these phases (mitosis)?

Answer 25

Prophase: breaks down, dissolves Telophase: nuclear envelope reforms, two new

Question 26

What phases are centrioles present in, and what happens in these phases (mitosis)?

Answer 26

Late interphase: centrioles replicate Prophase: move to opposite sides of cell Metaphase: reach poles, complete spindles

Question 27

What phases are centromeres present in, and what happens in these phases (mitosis)?

Answer 27

Metaphase: attatch to spindle by centromere Anaphase: centromere splits

Question 28

What phases are spindle fibres present in, and what happens in these phases (mitosis)?

Answer 28

Prophase: cytoskeleton protein fibres form spindle bwteen centrioles. 3D structure Metaphase: chromatids attatch to spindle threads at equator Anaphase: motor proteins walks along fibres, pull sister chromatids to opposite poles

Question 29

What phases are cell membranes present in, and what happens in these phases (in both animal and plant cells) (mitosis)?

Answer 29

Cytokinesis: - animal cells: plasma membrane folds inwards into cytoplasm - plant cells: end plate forms where equator was, new plasma membrane and cell wall. Wall material on either side of end plate

Question 30

Why is mitosis significant?

Answer 30

-Identical to parent -No genetic variation -Carry same information -Exact copies -Genetically identical -Clones -Advantageous characteristics inherited along with disadvantageous too, so suited to live in environment

Question 31

What happens in Prophase I (meiosis)?

Answer 31

Chromatin condenses, chromosomes appear Homologous chromosomes pair up, form bivalents Crossing over occurs between non sister chromatids

Question 32

What happens in Metaphase I (meiosis)?

Answer 32

Homologous pairs of chromosomes line up on cell equator, each attaches to a spindle fibre Orientation of each pair is random, called Independent Assortment

Question 33

What happens in Anaphase I (meiosis)?

Answer 33

Spindle fibres shorten and contract One homologous chromosome from each pair is pulled to either side of the cell

Question 34

What happens in Telophase I (meiosis)?

Answer 34

Nuclear membrane reforms Spindle breaks downn Chromosomes uncoil Two nuclei are visible, containing 1/2 the original number of chromosomes (n)

Question 35

What happens in Prophase II (meiosis)?

Answer 35

Chromosomes condense, become visible again Nuclear envelope breaks down Spindles begin to form

Question 36

What happens in Metaphase II (meiosis)?

Answer 36

Individual chromosomes assemble on metaphase plate Chromatids no longer identical due to crossing over, independent assortment and genetic variation occur once more

Question 37

What happens in Anaphase II (meiosis)?

Answer 37

Chromatids of individual chromosomes pulled to oppsite poles after division of centromeres

Question 38

What happens in Telophase II (meiosis)?

Answer 38

Chromatids assemble at poles Chromosomes uncoil and form chromatin again Nuclear envelope reforms, nucleolus becomes visible Cytokinesis divides into four daughter cells

Question 39

What is independent assortment?

Answer 39

Occurs during Metaphase I Chromosomes line up independently of one another, random pairs This mixes up the alleles that originally came from parent, so alleles mix Gives 2²³ possible combinations

Question 40

What are the advantages of asexual reproduction?

Answer 40

No mate required Quicker process to reach plant maturity All genetically identical, conserve favourable characteristics

Question 41

What are the disadvantages of asexual reproduction?

Answer 41

All genetically identical so equally vulnerable Conditions may change, no longer suitable and plants may die Grow close together, compete for resources

Question 42

What are advantages of sexual reproduction?

Answer 42

Genetic variation Adaptable to new conditions

Question 43

What are the disadvantages of sexual reproduction?

Answer 43

-Mate required -May not have advantageous characteristics -Slow

Question 44

What is differentiation?

Answer 44

The process by which the daughters of stem cells become specialised into different cell types by switching on/off different types of cell

Question 45

Why do multicellular organisms need to differentiate their cells?

Answer 45

Larger organisms have smaller SA:V Every cell not in contact with external environment and can't get what it needs by simple diffusion Division of labour, individual cells specialise in specific functions Cooperation between different cell types for several of organisms