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AS OCR Biology > Unit 2.6- Cell division, cell diversity and cell differentiation > Flashcards

Unit 2.6- Cell division, cell diversity and cell differentiation Flashcards

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1
Q

The cell cycle definition:

A

The series of events that take place in a cell leading up to its division an duplication of its DNA to produce two daughter cells

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2
Q

What are the different phases of the cell cycle?

A
  • M phase

- Interphase containing G0, G1, S, G2

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3
Q

What happens in the G0 phase of the cell cycle?

A
  • Cell death (apoptosis), differentiation or aging (senscence)
  • Some cells may remain in this stage for a long time
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4
Q

What happens in the G1 phase of the cell cycle?

A
  • Cells grow and increase in size
  • Transcription occurs
  • Organelles duplicate
  • Biosynthesis (protein synthesis) occurs
  • P53 (tumor suppressor) gene helps to regulate this phase. This regulates how much the cell grows
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5
Q

What happens in the S phase of the cell cycle?

A
  • DNA replicates
  • Formation of chromatids
  • Rapid completion of this phase because the exposed DNA base pairs are more susceptible to mutagenic agents, so this phase happening quickly reduces the chances of this
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6
Q

What happens in the G2 phase of the cell cycle?

A

The cell grows

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7
Q

What are the purposes of checkpoints in the cell cycle?

A
  • Prevent uncontrolled division that would lead to tumors
  • Detect and repair damage to DNA
  • To ensure the DNA is only replicated once during each cycle
  • To ensure the cycle happens in the right direction
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8
Q

What happens in the M phase of the cell cycle?

A
  • Cell growth stops
  • Nuclear division occurs
  • Cytokinesis (cytoplasmic division) occurs
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9
Q

What checkpoints happen in the M phase of the cell cycle?

A
  • A checkpoint chemical signals the condensation of chromatin
  • Halfway thought the cycle, the metaphase checkpoint ensures that the cell is ready to complete mitosis
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10
Q

What checkpoints happen in the G0 phase of the cell cycle?

A
  • A resting phase triggered during early G1 at the restriction point by a checkpoint chemical
  • Some cells such as epithelial cells lining the gut don’t have this phase
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11
Q

What checkpoints happen in the G1 phase of the cell cycle?

A

A G1 checkpoint control mechanism ensures that the cell is ready to enter the S phase and begin DNA synthesis

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12
Q

What checkpoints happen in the S phase of the cell cycle?

A

Every molecule of DNA is unwound and replicated. Genes that are active in every cell (housekeeping genes) are duplicated first. Genes that are normally inactive in specific types of cells are replicated last

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13
Q

What checkpoints happen in the G2 phase of the cell cycle?

A

Chemicals ensure that the cells is ready for mitosis by stimulating proteins that will be involved in making chromosomes condense and in the formation of the spindle

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14
Q

What are the different stages of mitosis?

A
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
  • (Cytokinesis)
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15
Q

What are the different stages of meiosis?

A
  • Prophase 1
  • Metaphase 1
  • Anaphase 1
  • Telophase 1
  • Prophase 2
  • Metaphase 2
  • Anaphase 2
  • Telophase 2
  • (Cytokinesis)
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16
Q

What happens in prophase in mitosis?

A
  • DNA supercoils
  • Nuclear envelope breaks down
  • The centriole in animal cells divides and the two new daughter centrioles move to opposite poles of the cell
  • Tubulin threads form a spindle between these centrioles. In plant cells the tubulin threads are formed from the cytoplasm
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17
Q

What happens in metaphase in mitosis?

A

The pairs of chromatids attatch to the spindle threads at the equator region by their centromeres

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18
Q

What happens in anaphase in mitosis?

A
  • The centromere of each pair of chromatids splits
  • Motor proteins walk along the tubulin threads, pulling each sister chromatid of a pair in opposite directions
  • Because their centromere goes first, the chromatids, now called chromosomes assume a V shape
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19
Q

What happens in telophase in mitosis?

A
  • The separated chromosomes reach the poles
  • A new nuclear envelope forms around each set of poles
  • The cell now contains two nuclei
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20
Q

What happens in cytokinesis after mitosis?

A
  • The cell splits into two
  • In animal cells the plasma membrane folds inwards and ‘nips in’ the cytoplasm
  • In plant cells an end plate forms where the equator of the spindle was and new plasma membrane and cellulose cell wall material are laid down along this end plate
  • Two new daughter cells are now formed
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21
Q

Homologous chromosomes definition:

A

Matching chromosomes, containing the same genes at the same loci. They may contain different alleles for some of the genes.

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22
Q

Haploid definition:

A

Having only one set of chromosomes. Diploid has two.

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23
Q

What happens in phrophase 1 in meiosis?

A
  • Chromatin condenses and each chromosome supercoils
  • The nuclear envelope breaks down
  • Spindle threads of tubulin proteins form from the centrioles in animal cells
  • Chromosomes come together in their homologous pairs and crossing over occurs where non-sister chromatids wrap around each other and may swap sections so that alleles are shuffled
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24
Q

What happens in metaphase 1 of meiosis?

A
  • Pairs of homologous chromosomes, still in their crossed over state attach along the equator of the spindle by their centromeres.
  • The homologous pairs are arranged randomly. This arrangement is independent assortment
  • The way they line up in metaphase will determine how they will segregate when pulled apart in anaphase
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25
Q

What happens in anaphase 1 of meiosis?

A
  • The members of each pair of homologous chromosomes are pulled apart by motor proteins that pull them along tubulin threads.
  • The centromeres do not divide and each chromosome consists of two chromatids
  • the crossed over areas separate from each other, resulting in allele shuffling
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26
Q

What happens in telophase 1 in meiosis?

A
  • In most new animal cells, two new nuclear envelopes form around each set of chromosomes and the cell divides by cytokinesis. Then there is a short interphase where the chromosomes uncoil
  • Each new nucleus contains half the number of chromosomes, but each chromosome consists of two chromatids
  • Most plant cells skip this stage
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27
Q

What happens in phrophase 2 of meiosis?

A
  • If the nuclear envelopes had reformed, they now break down
  • The chromosomes supercoil, each one consisting of two chromatids
  • Spindles form
28
Q

-What happens in metaphase 2 of meiosis?

A
  • The chromosomes attach by their centromeres to the equator of the spindle
  • The chromatids of each chromosome are randomly arranged. This will determine how the chromatids separate during anaphase
29
Q

-What happens in anaphase 2 of meiosis?

A
  • The centromeres divide
  • The chromatids of each chromosome are pulled apart by motor proteins walking along tubulin threads towards opposite poles
  • The chromatids are therefore randomly segregated
30
Q

-What happens in telophase 2 of meiosis?

A
  • Nuclear envelopes form around the 4 haploid nuclei
  • Each nuclei contains single chromatids
  • In animals, the cells divide to give 4 cells
  • In plants, a tetrad of 4 haploid nuclei is formed
31
Q

How does meiosis cause genetic variation?

A
  • Crossing over during phrophase 1 shuffles alleles
  • Independent assortment of chromosomes in anaphase 1 leads to a random distribution of maternal and paternal chromosomes of each pair
  • Independent assortment in anaphase 2 leads to further random distribution of genetic material
  • The haploid gametes produced can undergo random fusion with gametes derived from another organism of the same species
32
Q

Erythrocyte definition:

A

Red blood cell

33
Q

Neutrophil definition:

A

Type of white blood cell that is phagocytic

34
Q

How is the division of labour determined in single celled organisms?

A

It is split into different jobs by different organelles.

35
Q

Genome definition:

A

The genetic material in an individual

36
Q

Gene pool definition:

A

The genetic material within a populationn

37
Q

What happens when embryonic cells differentiate?

A

Certain genes are switched off and others are expressed more so that:

  • The proportions of the different organelles differs from other cells
  • The shape of the cell changes
  • Some of the contents of the cell change
38
Q

How are erythrocytes specialised to carry out their function?

A
  • Very small (7.5 um in diameter) and have a biconcave shape so have a large SA/V ratio. This allows oxygen to diffuse across their membrane and reach all regions inside the cell.
  • Flexible. A well developed cytoskeleton allows them to twist and turn so they can move down the narrow capillaries.
  • Most of their organelles are lost at differentiation, which provides more space for haemoglobin molecules to be housed inside them.
39
Q

When is haemoglobin synthesised in RBCs?

A

In immature erythrocyes, when they still have their nucleus, ribosomes and RER

40
Q

How are neutrophils adapted to carry out their function?

A
  • They are about twice the size of erythrocytes and contain a multilobed nucleus.
  • They are attracted to and travel towards sites of infection by chemotaxis
  • Their function is to ingest bacteria (and some fungi) by phagocytosis
41
Q

How are spermatozoa specialised?

A
  • There are many mitochondria to carry out aerobic respiration. The ATP provides energy for the undulipodium to move and propel the cell towards the ovum
  • They are small but long and thin so can move easily
  • Once the sperm reaches the ovum, enzymes are released from the acrosome (a specialised lysosome). The enzymes digest the outer protective covering of the ovum, allowing the sperm head to enter the ovum.
  • The head of the sperm contains the haploid male gamete nucleus and very little cytoplasm
42
Q

Epithelial cells definition

A

Lining tissue. Makes up the walls of the alveoli and the capillaries and lines the intestines.

43
Q

How are epithelial cells specialised?

A
  • Squamous epithelial cells are flattened in shape

- Many epithelial cells have cillia

44
Q

Guard cells definition:

A

In leaf epidermis, cells that surround stomata

45
Q

Palisade cells definition:

A

Closely packed, photosynthetic cells within leaves

46
Q

Root-hair cells definition:

A

Epidermal cells of young roots with hair-like projections

47
Q

How are palisade cells within leaves adapted for photosynthesis?

A
  • Long and cylindrical so there is little space between them, but enough for air to circulate and carbon dioxide in these spaces can diffuse into the cells
  • Large vacuole so the chloroplasts are nearer the edge of the cell, reducing the diffusion distance for carbon dioxide
  • Contain many chloroplasts
  • Contain cytoskeleton threads and motor proteins to move the chloroplasts nearer to the upper surface of the leaf when sunlight intensity is low, and further away when it is high
48
Q

Why can guard cells not carry out photosynthesis?

A

Although they contain chloroplasts, they do not have the enzymes needed for the second stage of the process

49
Q

How do guard cells enable gaseous exchange?

A
  • Light energy is used to produce ATP
  • The ATP actively transports potassium ions from surrounding epidermal cells into the guard cells, lowering their water potential
  • Water now enters the guard cells from neighbouring epidermal cells by osmosis
  • The guard cells swell, but the cell wall is more flexible and the tips, and more rigid where it is thicker. The tips bulge and the gaps between them (stoma) enlarges.
  • As the stomata open, air can enter spaces within the layer of cells beneath the palisade cells
  • Gaseous exchange will occur and carbon dioxide will diffuse into the palisade cells. As they use it for photosynthesis, this will maintain a steep concentration gradient.
  • Oxygen produced during photosynthesis can then diffuse out of the stomata
50
Q

How is the shape of a root hair cell beneficial?

A

The hair-like projection greatly increases the surface area for absorption of water and mineral ions such as nitrates from the soil into which it projects

51
Q

How do mineral ions influence the water potential gradient in root hair cells?

A

Mineral ions are actively transported into root hair cells. This causes the water potential in the cells to decrease, so water enters the cells through osmosis

52
Q

How are root hair cells adapted to allow mineral ions to enter the cells?

A

They have special carrier proteins in the membrane to actively transport the minerals in.

53
Q

Why do root hair cells produce ATP?

A

It is needed for active transport

54
Q

What are the four main types of tissue our body has?

A
  • Epithelial: lining tissue
  • Connective tissues: Hold structures together and provide support e.g. blood, bone and cartilage
  • Muscle tissue: Made of cells that are specialised to contract and cause movement
  • Nervous tissue: Made of cells specialised to conduct electrical impulses
55
Q

Where does epithelial tissue cover?

A

The free surfaces in the body such as the skin, cavities of the gut and airways, blood vessels, heart chambers and walls of organs

56
Q

What are the characteristics of epithelial tissue?

A
  • Made up almost entirely of cells
  • These cells are very close together and form continuous sheets. Adjacent cells are bound together by lateral contacts such as junctions and desmosomes
  • There are no blood vessels, cells receive nutrients by diffusion from tissue fluid
  • Some epithelial cells have smooth surfaces, others have projections such as cilia or microvilli
  • They have short cell cycles and divide up to two or three times a day to replace worn or damaged tissue
  • Specialised to carry out its function of protection, absorption, filtration, excretion and secretion
57
Q

What does connective tissue consist of?

A

A non-living extracellular matrix containing proteins (collagen and elastin) and polysaccharides (such as hyaluronic acid, which traps water)

58
Q

What does the matrix in connective tissue do?

A

Separates the living cells within the tissue and enables it to withstand forces such as weight.

59
Q

Chondroblasts definition:

A

Immature cells in cartilage

60
Q

What can chondroblasts do?

A

Divide by mitosis and excrete the extracellular matrix in cartilage, Once the matrix has been synthesised, the chondroblasts become mature, less active chondrocyes which maintain the matrix.

61
Q

Chondrocytes definition:

A

Less active, mature, chondroblasts. (The cells in cartilage.)

62
Q

What are the three types of cartilage?

A
  • Hyaline
  • Fibrous
  • Elastic
63
Q

Where does hyaline cartilage occur?

A
  • Forms the embryonic skeleon
  • Covers the ends of long bones in adults
  • Joins ribs to the sternum
  • Found in the nose
  • Forms the C shaped rings in the trachea
  • Found in the larynx (voice box)
64
Q

Where does fibrous cartilage occur?

A

Discs between vertebrae in the backbone and in the knee joint.

65
Q

Where does elastic cartilage occur?

A
  • Outer ear (pinna)

- Epiglottis (flap that closes over the larynx when you swallow)

AS OCR Biology (12 decks)

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