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A level Biology > 2.6 cell division and diversity > Flashcards

2.6 cell division and diversity Flashcards

1
Q

state what the cell cycle is and outline its stages

A

It is a regulated cycle of division with intermediate growth periods

Interphase
mitosis/meiosis
cytokenesis

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2
Q

outline what happens during interphase

A

G0 - cells may undergo apoptosis (programmed cell death), It is a resting phase triggered during early G1

G1 - cell synthesises proteins for replication and cell size doubles

S - DNA replicates = chromosomes consist of 2 sister chromatids joined at a centromere

G2 - organelles divide

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3
Q

what is the purpose of mitosis

A

produces 2 genetically identical cells for
growth
repair
asexual reproduction

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4
Q

name the stage of mitosis

A

Prophase
Metaphase
Anaphase
Telophase

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5
Q

outline what happens during prophase

A

chromosomes condense, becoming visible

centrioles move to opposite poles of cell and mitotic spindles form

Nuclear envelope and nucleolus break down so chromosomes are free in the cytoplasm

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6
Q

outline what happens during metaphase

A

sister chromatids line up at the cell equator, attaches to the mitotic spindles by the centromeres

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7
Q

outline what happens during anaphase

A

spindle fibres contract and centromeres divide

sister chromatids sperate into 2 distinct chromosomes and are puled to opposite poles of the cell

spindle fibres break down

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8
Q

outline what happens during telophase

A

chromosomes decondense becoming non-visible again

new nuclear envelopes form around each set of chromosomes each are genetically identical

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9
Q

how is the cell cycle regulated?

A

Checkpoints regulated by cell signalling proteins ensure that damaged cells don’t progress to the next stage.

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10
Q

What is meiosis?

A

Type of nuclear division that results in the formation of cells containing half the number of chromosomes found in the parent cell.

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11
Q

What is the significance of meiosis in the life cycle?

A

During sexual reproduction the gamete cells only need half the normal amount of chromosomes (haploid cells)

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12
Q

Define homologous pairs.

A

A homologous pair of chromosomes has the same genes and all of the same alleles of that gene will appear at similar locations (locus) on that chromosome.
Although they may have the same genes their alleles can be different.

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13
Q

How many chromosomes and chromatids are there in the cell before and after meiosis?

A

Chromosomes:
before 46
after interphase 46
after meiosis 1 23
after meiosis 2 23

Chromatids:
before 46
after interphase 92
after meiosis 1 46
after meiosis 2 23

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14
Q

Define bivalent and chiasma.

A

pair of homologous chromosomes

chiasma - point of contact between bivalents

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15
Q

What are the 4 differences between meiosis and mitosis?

A

1- Meiosis produces genetically different haploids
2- meiosis has 2 divisions whereas mitosis has only 1
3- meiosis produces 4 haploids for sexual reproduction with 23 chromosomes. Whereas, mitosis produces 2 genetically identical cells with 46 chromosomes for asexual reproduction and growth and repairs
4- No bivalent in mitosis so chiasma don’t form.

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16
Q

Outline what happens in prophase 1.

A

The nuclear envelope breaks down and chromosomes condense, which then come together in their homologous pairs.
Crossing over occurs here where non-sister chromatids wrap around each other and may swap sections so that alleles are shuffled.

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17
Q

Outline what happens in metaphase 1.

A

The homologous pairs align at the equator at the cell and each attaches to a spindle thread by its centromere.

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18
Q

Outline what happens in anaphase 1.

A

The members of each pairs are pulled apart by motor proteins that drag them along the spindle threads.
The centromeres do not divide and each chromosome consists of two chromatids.

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19
Q

Outline what happens in telophase 1.

A

The nuclear envelope reforms and the 2nd division starts

20
Q

Outline what happens in prophase 2.

A

The nuclear envelope breaks down, chromosomes condense (no longer identical) and spindles form.

21
Q

Outline what happens in metaphase 2.

A

Chromosomes align at the equator of the cell and attach to spindles by their centromeres.

22
Q

Outline what happens during anaphase 2.

A

The spindles contract and the centromeres divide.

23
Q

Outline what happens during telophase 2.

A

4 Haploid cells are formed and nuclear envelope forms around each 4 nuclei

24
Q

How does meiosis create genetic variaiton?

A

Crossing over during prophase 1 shuffles alleles.

Independent assortment of chromosomes in anaphase 1 leads to random distribution of maternal and paternal chromosome of each pair.

Independent assortment of chromatids in anaphase 2 leads to further random distribution of genetic material.

Random fusion of gametes.

25
Q

How do cells become specialised?

A

Some genes are expressed while some are silenced due to cell differentiation mediated by transcription factors.
The cell then produces proteins which that determines their structure and function.

26
Q

What is a transcription factor?

A

A protein that controls the transcription of genes so that only certain parts of DNA are able to be expressed

27
Q

What is a stem cell?

A

An undifferentiated cell where all of the alleles are able to be expressed.

28
Q

Name and define the 4 types of stem cells.

A

totipotent- can develop into any type of cell
pluripotent-can develop into any type of cell except embryo and placenta
multipotent- can develop into some different types of cells
unipotent- can develop into only one type of cell

29
Q

Suggest some uses of stem cells.

A

Repair of damaged tissues.
Drug testing on artificially developed tissue
To treat neurological disorders e.g. Alzheimer’s
Researching developmental biology

30
Q

Describe the 2 groups of specialised cells in the blood.

A

Erythrocytes-biconcave, no nucleus lots of haemoglobin to carry oxygen
leucocytes- lymphocytes neutrophils and eosinophils to engulf foreign materials. Monocytes

31
Q

How do the specialised cells in the blood form?

A

The multipotent cells in the bone marrow differentiate into erythrocytes and leucocytes including neutophils.

32
Q

Describe the structure of squamous and ciliated epithelial.

A

squamous - single smooth layer of squamous cells fixed in place by basement membrane

ciliated- made of ciliated epithelial cells

33
Q

Describe the specialised structure of a spermatozoon.

A

lots of mitochondria.
Haploid nucleus
flagellum to propel the cell
acrosome secretes enzyme to penetrate ovum coat

34
Q

Describe the structure and function of palisade cells in plants

A

Well adapted for photosynthesis because they have many chloroplasts which are situated on the cells periphery (due to large vacuole) which decreases diffusion distance.
Also contains cytoskeleton threads and motor proteins in order to move chloroplast nearer to the surface when there isn’t a lot of sun.

35
Q

Describe the structure and role of guard cells.

A

The are involved in gas exchange.
Potassium ions are actively transported from the surrounding cells into the guard cells lowering their water potential, causing water to enter the cell by osmosis making it swell and bulge and the gap between them enlarges.

36
Q

Describe the structure and function of root hair cells.

A

The hair like projection greatly increases surface area for greater absorption of water and mineral ions.

37
Q

What are meristems?

A

Totipotent undifferentiated plant cells which can differentiate into many different cells including phloem sieve tubes and xylem vessels

38
Q

Describe the structure of phloem tissue.

A

Meristem produces cells that elongate and line up end to end to form a long tube.
It has 2 way flow and companion cells(which helps with ATP)
(glucose and water)

39
Q

Describe the structure of the xylem.

A

Meristem cells produce small cells which elongate and the walls become reinforced with lignin
Large lumen
(water and minerals)

40
Q

Name the 3 types of muscle and where they are located.

A

Cardiac - heart
smooth - walls of blood vessels and intestines
skeletal - attached to incompressible skeleton by tendons

41
Q

What are the 4 types and tissue and their function.

A

Epithelial - lining tissue
muscle- contract and cause movement
connective- hold structures together and provide support e.g. cartilage
nervous- conduct electrical impulses

42
Q

what is the function of epithelial tissue

A

lining free surfaces

43
Q

what is the function of connective tissue

A

to hold structures together and provide support
fibrocartilage - vertebral discs
elastic- ear and epiglottis
hyaline - bones and trachea

44
Q

what are some sources of stem cells

A

embryos umbilical cord adult stem cells
IPS - induced pluripotent stem cells in the lab

45
Q

how does a cell begin to differentiate

A

cell shape changes
cell content changes
proportion of organelles changes

46
Q

how are guard cells adapted

A

control opening of stomata cell wall around stoma thicker and more rigid and lots of carrier proteins in the membrane

A level Biology (25 decks)

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