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Wjec A Level Biology > Unit 4 Mixed > Flashcards

Unit 4 Mixed Flashcards

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1
Q

What is the advantage of preventing self-pollination

A

Increases genetic variation and so increases the chances of survival of the species as it can adapt to a changing environment

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2
Q

Why is an even number of chromosomes needed to make a species fertile

A

Homologous pairs and bivalents can form during prophase 1 of meiosis and so gametes can be produced

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3
Q

Intron

A

Non coding region of DNA
is spliced out and not translated

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4
Q

Exon

A

Coding regions which are translated for a polypeptide

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5
Q

What are the potential problems of using a virus in gene therapy

A

Can cause an immune response
May not reach the target cell
May become pathogenic
May affect other genes - oncogenes

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6
Q

What are the disadvantages of using a molecular patch to treat DMD

A

• it is not permanent and so repeated treatments are needed
• the change is not present after cell replication and so is not passed onto next generation

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7
Q

Ethical issues of germ line therapy

A

• unknown long term effects
• possible activation of oncogenes
• the modified genes are passed onto the next generation and so will effect later generations

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8
Q

Antigen

A

Innates an immune response and the production of antibodies

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9
Q

What is an antigen-antibody complex

A

When a specific antibody is bound to an antigen

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10
Q

How can the sperm enter the secondary oocyte

A

Acrosome reaction
The acrosome releases hydrolytic enzymes such as proteases which hydrolyse the corona radiata and zona pellucide

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11
Q

How is polyspermy prevented

A

Cortical reaction
The cortical granules rupture and the zona pellucida thickens and hardens to form the fertilisation membrane

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12
Q

Continuous variation

A

Polygenic
Imtermediates

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13
Q

Discontinuous variation

A

Monogenic
Distinct groups

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14
Q

How does natural selection work

A

• variation is caused due to mutations
• some mutations will confer a selective advantage
• individuals with selective advantage is more likely to survive and reproduce and pass on advantageous alleles to offspring
• this is repeated over several generations and the allele frequency of the advantageous allele will increase

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15
Q

Sympatric speciation

A

Non-geographical barriers

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16
Q

Allopatric speciation

A

Geographical barriers

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17
Q

How do isolation barriers work

A

• prevent the gene flow
• genetic differences will accumulate and so they can no longer produce fertile offspring

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18
Q

Umbilical artery

A

Carries blood away from foetus
Contains carbon dioxide, urea

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19
Q

Umbilical vein

A

Carries blood to the foetus
Contains oxygen, nutrients and antibodies

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20
Q

Ethics of prenatal diagnosis

A

• more selective abortions
• moral status of the foetus
• may cause harm to foetus
• may give a false negative

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21
Q

Conditions required for germination and why

A

• water - cause cotyledons to swell and to dissolve substances to act as a fluid medium for enzymes
• oxygen - for aerobic respiration to produce ATP for metabolism
• suitable temperature- to increase rate of diffusion and to increase enzyme activity

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22
Q

Germination of non-endospermic seeds

A

• endosperm has been absorbed into cotyledons
• amylase digest starch in the cotyledons to maltose
• proteins and fats are also broken down into amino acids, fatty acids and glycerol
• these move into the plumule and radicle and are used for cell division for growth

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23
Q

Germination of endospermic seed

A

• starch, proteins and fats are in the endosperm
• the embryo produces gibberellin which moves into the aleurone layer
• the GA causes enzymes to break down proteins into amino acids which are used to synthesise other proteins such as amylase which breaks down starch in the endosperm into maltose

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24
Q

What is gene therapy

A

The treatment of genetic disease by replacing defective alleles in a patient with copies of a new DNA sequence

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25
Q

Somatic cell therapy

A

• therapeutic genes are transferred into somatic cells
• the modification and effects are restricted to the individual only and cannot be passed on through gametes
• DNA is introduced into the target cells by a vector such as plasmid or virus

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26
Q

Germ line therapy

A

• sperm or egg is modified
• allows therapy to be heritable
• rare due to ethical and technical reasons

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27
Q

Gene therapy to treat Duchenne muscular dystrphy

A

Use of the drug disapersen
Exon skipping - a molecular patch is introduced over the exon with the mutation which makes the gene readable again
• a shorter form of dystrophin is produced but it is more functiona

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28
Q

What is tissue engineering

A

The study of growth of new connecting tissues or organs from cells and a collagenous scaffold to produce a fully functional organ for implantation back into the donor host

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29
Q

Scaffolds used in tissue engineering

A

• artificial structures that support 3D tissues
• allow cells to attach and move
• deliver and retain cells and biological molecules
• are porous to allow diffusion of nutrients and waste
• biodegradable and can be adsorbed by the surrounding tissues

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30
Q

What is a stem cell

A

An undifferentiated cell capable of dividing to give rise to daughter cells which can develop into different types of specialised cell or remain as undifferentiated stem cells

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31
Q

Sources of stem cells

A

Embryos and bone marrow

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32
Q

Embryonic stem cells

A

Totipotent so can differentiate into all types of cells

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33
Q

Adult stem cells

A

Pluripotent so cannot differentiate into all types of cells

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34
Q

What is recombinant DNA

A

DNA produced by combining DNA from 2 different species

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35
Q

What are restriction enzymes

A

Bacterial enzymes that cut up any foreign DNA that enters a cell
Cut is staggered with short, single-stranded fragments called sticky ends at either ends

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36
Q

How to a gene inserted into a plasmid using restriction enzymes

A
  1. Bacterial plasmid contains 2 marker genes (one for ampicillin resistance and the other that is rendered non-functional if DNA is successfully inserted into it)
  2. Plasmid is cut open using a restriction enzyme
  3. Foreign DNA is cut with the same restriction enzyme to ensure complementary sticky ends
  4. DNA is inserted using DNA ligase which joins the sugar backbone of the 2 sections of the DNA together
  5. Ensure bacteria have a plasmid with a donor gene
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37
Q

Preparing a fragment of DNA containing a human gene using reverse transcriptase

A
  1. Reverse transcriptase produces a complimentary or cDNA from a mENA template
  2. A human regulator sequence which controls gene expression is replaced by a bacterial regulator and so the cDNA is inserted
  3. Once expressed in bacterial cells the insulin can be purified for use
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38
Q

What problems does producing cDNA overcome

A

• locating the gene
• restriction enzymes cutting the gene into non-functional fragments
• the presence of introns as prokaryotes dont have introns
• the need for post-transcriptional processing to produce functional mRNA

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39
Q

Advantages of genetically engineered bacteria

A

• allows for the production of complex proteins or peptides which cant be made by other methods
• can be used to produce medicinal products such as insulin

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40
Q

Disadvantages of genetically engineered crops

A

• is complicated and expensive
• can be hard to indentify genes in a genome
• the synthesis of a required protein may involve many genes each coding for a polypeptide
• using restriction enzymes produces millions of non-useful fragments
• not all eukaryotic genes will express themselves in a prokaryotic cell

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41
Q

Hazards of genetically engineered bacteria

A

• bacteria can readily exchange DNA and so antibiotic resistance could be transferred to pathogens
• the possible transfer of oncogenes

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42
Q

Advantages of GM crops

A

• better keeping qualities
• higher yield due to the increased growth rates, improved nutritional value, ease of management, tolerance of unfavourable conditions
• less pesticide use due to resistance of pathogens and insects

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43
Q

Disadvantages of GM crops

A

• genetic contamination - herbicide resistance could spread to wild relatives and form superweeds
• misuse of pesticides
• corporations controlling agriculture

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44
Q

Hazards of GM crops

A

• reduces biodiversity by changing natural gene pools
• there are unknown effects of eating new protein

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45
Q

Advantages of stem cells

A

• can be produced quickly and on a large scale
• produces genetically identical cells for transplant which reduces the risk of rejection

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46
Q

Disadvantages of stem cells

A

• expensive and unreliable
• unknown long term effects
• inadvertent selection of disadvantageous alleles

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47
Q

Ethics of stem cells

A

• an embryo mist be destroyed to obtain the cells
• may be used for non-medical purposes

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48
Q

State the function of the tapetum

A

Provides nutrients for the developing pollen
Provides a waterproof outer coat for the pollen grains

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49
Q

Function of tube nucleus in growth of pollen tube

A

Controls the pollen tube
Controls the synthesis of hydrolytic enzymes

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50
Q

Role of mitosis and meiosis in the formation of the female gamete

A

• megaspore mother cell undergoes meiosis
• forms four haploid cells
• one of these cells undergoes three mitotic divisions
• one of the these cells become the oosphere, 2 fuse and produce a diploid polar nucleus, 3 form antipodals and 2 form synergids

51
Q

Why is fertilisation in plants referred to as double fertilisation

A

• one male gamete fuses with the oosphere to produce a diploid zygote
• the other male gamete fuses with the diploid polar nucleus to produce a triploid endosperm nucleus

52
Q

What information has been obtained from the Anopheles and Plasmodium Genome Projects

A

• the DNA sequence code
• the location of genes on chromosomes
• the complete DNA sequence

53
Q

Uses of the information obtained from the genome projects of Anopheles and Plasmodium l

A

• make plasmodium susceptible to insecticides
• make mosquitoes less fertile
• prevent transmission
• modification of Plasmodium to reduce pathogenticity
• development of more effective drugs or vaccines

54
Q

Proto-oncogene

A

Genes which can mutate to oncogenes which cause cancer

55
Q

What is epigenetics

A

The control of gene expression

56
Q

What is a stem cell

A

An undifferentiated cell that has the ability to become specialised cells

57
Q

How does DNA methylation result in tumour growth

A

mRNA from regulator not produced so regulator protein not produced
The suppressor gene is not expressed so there is uncontrolled cell division

58
Q

How do cancer cells switch the suppressor genes off

A

Remove acetyl groups from histones so the DNA becomes tightly coiled and so RNA polymerase can’t access the gene and so cannot be transcribed

59
Q

What is the consequence of tumor suppressor genes becoming permanently switched off in all cells in the body

A

Increases the risk of cancer which can be passed onto the next generations

60
Q

FSH

A

Follicle development

61
Q

LH

A

Causes ovulation

62
Q

Role of prolactin in women

A

Stimulates cells in mammary glands to secrete milk into ducts

63
Q

Why is oxytocin production during birth is an example of positive feedback

A

• stimulates contraction of myometrium which stimulates the release of more oxytocin which increases the contractions

64
Q

How a cDNA fragment containing a human gene can be prepared

A

• extract mRNA from the bacterium
• use reverse transcriptase to synthesise a single strand of cDNA using the mRNA as a template
• use DNA polymerase to produce double stranded DNA
• add sticky ends to ends of each DNA strand of the DNA
• copy the DNA many times using PCR

65
Q

How does genetically engineered plasmids be produced

A

• plasmids from a bacteria are isolated
• restriction enzyme such as restriction endonuclease is used to open the plasmid at a specific point which produces sticky ends which are complementary to the DNA
• DNA ligase is used to bind the DNA into the plasmid
• antibiotic resistance marker genes are used to select bacteria containing the recombinant plasmids

66
Q

Natural barriers to infection in the body

A

• ciliated mucous membranes
• skin microflora
• lysozyme in tears, saliva and mucus
• low stomach pH
• skin connective tissue
• inflammation- blood clotting, phagocytes

67
Q

Why is the body sometimes described as a host to other living organisms

A

Many organisms live in or on the human body

68
Q

How do phagocytes and T lymphocytes bring about the cell-mediated response against a virus

A

• macrophages engulf the virus infected cell by phagocytosis and present the antigen on their surface
• colonal expansion of T cells causes their proliferation into T helper, T killer and T memory
• T killer cause cell lysis
• cytokines stimulate phagocytosis

69
Q

Why can antibiotics be used to treat bacterial infections and not viral infections

A

• antibiotics act on cell walls of bacteria
• antibiotics affect the metabolism carried out by bacteria
• viruses do not have cell walls or a metabolism and so are not affected by antibiotics

70
Q

Why is it unlikely that a vaccine for the common cold will ever be developed

A

• high mutation rate and so there are many strains and antigenic types
• vaccines need to contain antigens from all strains to provide complete immunity
• each antigen must produce a strong immune response

71
Q

Why is it unethical to make the flu vaccine compulsory for all

A

• religious objections
• fears of safety and side effects
• individual rights
• some may be too ill for vaccination due to HIV or chemotherapy

72
Q

Where does spermatogenesis occur

A

Seminiferous tubules

73
Q

Process of spermatogenesis

A

Germinal epithelium cells (2n) divide by mitosis to form spermatogonia (2n) which divide by mitosis to form primary spermatocytes (2n) these undergo meiosis I to form secondary spermatocytes (n) which undergo meiosis II to form spermatids (n) which mature into spermatozoa (n)

74
Q

Function of interstitial cells

A

Secrete testosterone which stimulates the process of spermatogenesis

75
Q

Function of steroli cells

A

Provide nourishment and protection to cells during spermatogenesis

76
Q

Head of a sperm

A

About 5um
• haploid nucleus
• acrosome

77
Q

Midpiece of sperm

A

Contains lots of mitochondria to provide ATP for movement

78
Q

Tail of sperm

A

50 um
• moves in a circular motion to propel

79
Q

Where does oogenesis occur

A

• in the ovary up until the secondary oocyte

80
Q

Process of oogenesis

A

Before birth
• germinal epithelium cells (2n) undergo mitosis to form oogonium (2n) which undergo mitosis to form Primary oocyte (2n) which undergoes meiosis I up until prophase I

After puberty
• meiosis I is complete and a secondary oocyte (n) and a first polar body is produced (n). The secondary oocyte undergoes meiosis II up until metaphase II

After fertilisation
• meiosis II completes and an ovum (n) and a second polar body (n) is produced

81
Q

What surrounds primary oocytes

A

Germinal epithelium cells which form the primary follice

82
Q

What surrounds the secondary oocyte

A

The primary follicle develops into a secondary follicle which matures to a Graafian follicle which migrates to the surface and bursts which releases the secondary oocyte

83
Q

What happens to Graafian follice when it is an ovum

A

Becomes the corpus luteum

84
Q

Process of fertilisation

A
  1. Spermatozoa move into the Fallopian tubes
  2. Capacitation - cholesterol and glycoproteins are removed from the cell membrane over the acrosome which increases the permeability of the membrane
  3. Acrosome reaction - protease is released and digests the corona radiata. Once the sperm head is in contact with the zona pellucida the acrosome ruptures and releases acrosin which hydrolyses the zona pellucida
  4. Sperm head entry - cell membrane of the sperm and oocyte fuse and the male nucleus starts to enter the oocytes cytoplasm
  5. Cortical reactions - cortical granule membrane fuse with oocyte cell membrane and the membrane expands and hardens to form the fertilisation membrane which prevents polyspermy
  6. 2nd meiotic division completes and the ovum is formed
  7. Mitosis occurs as material is combined to make diploid cells of the embryo called a zygote
85
Q

What is implantation

A

Sinking of the blastocyst into the endothelium

86
Q

Process from fertilisation to implantation

A

• cleavage - the zygote undergoes repeated mitotic division to form a ball of 16 cells called a morulla by day 3
• by day 7 a blastocyst forms and has an outer layer of cells called a trophoblast which develops trophoblastic villi which penetrate the endometrium and increases the surface area for absorption of nutrients from the endometrium

87
Q

Implantation window

A

The endometrium is receptive to accept implantation of the blastocyst as the endometrium is thick
About 8-10 days post ovulation

88
Q

Process of double fertilisation

A

• a compatible pollen grain lands on the stigma and germinates in the sucrose solution secreted by stigma and a pollen tube is produced
• the pollen tube grows out of the pollen grain through a pit, down the style and up a gradient of chemoattractants.
• the pollen tube nucleus codes for the production of hydrolases (cellulases and proteases) and digests its way through the tissues of the style and the products of digestion is used by the growing pollen tube
• the pollen tube grows through the micropyle and passes into the embryo sac
• the pollen tube nucleus then disintegrates and the tip of the tube opens to release the 2 male gametes into the embryo sac
• first male gamete enters the embryo sac and fuses with the oocyte to form a diploid zygote
• second male gamete fuses with the diploid polar nucleus and forms a triploid primary endosperm nucleus

89
Q

Dicotyledons

A

Eg broad beans
• non-endospermic seeds as the endosperm is absorbed into the cotyledons

90
Q

Monocotyledons

A

Eg maize
Endospermic seed
Endosperm is the food source

91
Q

Plumule

A

Developing shoot

92
Q

Radicle developing root

A
93
Q

Why must seedlings be moved away from the parent plant

A

Seedling would be outcompeted by more successful parents which can obtain water and minerals from soil and cast a shade over the seedling

94
Q

Non-endospermic germination

A

• water is embibed through the micropyle which causes the cotyledons to swell so the testa splits so more oxygen can diffuse in for respiration
• starch and proteins in the cotyledons are mobilised through hydrolysis into maltose and amino acids
• these products provide energy for the plumule and radicle for growth

95
Q

Endospermic germination

A

• water absorbed through micropyle
• gibberellin in the cotyledon are released by the embryo and diffuse into the aleurone layer
• GA induces the transcription of DNA and the mRNA is translated into hydrolytic enzymes
• proteases hydrolyse proteins into amino acids which are used to form amylase and maltase
• amylase diffuses out of the aleurone layer and hydrolyses starch in the endosperm into maltose then glucose
• these diffuse to embryo where radicle and plumule use glucose for aerobic respiration

96
Q

Pollen grain development

A

Diploid mother cell undergoes meiosis to form a tetrad of 4 haploid pollen cells
Each of these undergo mitosis to form a generative nucleus and a tube nucleus
The generative nucleus undergoes mitosis to form 2 male nuclei

97
Q

Function of tapetum

A

A specialised layer of nutritive cells which provides nutrition to developing pollen grains

98
Q

What is dehiscence

A

The opening of the anther which releases the pollen grains

99
Q

Process of dehisence

A

Anther outer layers mature and dry out so outer walls curl away which exposes the pollen grains
The lateral grooves open up and form a gap called the stomeum
The pollen sacs are opened

100
Q

Where is ovule produced

A

Ovary

101
Q

Another word for ovule

A

Megaspore

102
Q

Where are female gametes formed

A

Within embryo sac within nucellus

103
Q

Process of ovule development

A

• megaspore mother cell (2n) undergoes meiosis to produce 4 haploid cells
• 3 degenerate
• 1 of the haploid cells undergo 3 mitotic divisions to form 8 haploid cells
• 2 combine to form a diploid polar nucleus, 3 form antipodals, 2 syngerids and 1 forms the oosphere

104
Q

What is pollination

A

The transfer of pollen grains from the anther to the mature stigma of a plant from the same species

105
Q

What is self-pollintation

A

When a pollen is transferred to the stigma of the same plant

106
Q

What is cross-pollination

A

When pollen from one plant is transferred to the stigma of a different plant

107
Q

How is cross-pollination promoted

A

• chemical self-incompatibility
• dichogamy

108
Q

Dichogamy

A

Stamen and stigma ripen at different times

109
Q

Protandry

A

Stamen ripens first

110
Q

Protogyny

A

Stigma ripens first

111
Q

Follicle stimulating hormone

A

• stimulates maturation of follicle
• stimulates oestrogen production
• is secreted by anterior pituitary gland

112
Q

Luteinising hormone

A

Initiates ovulation
Stimulates the formation of the corpus luteum
Inhibits oestrogen
Secreted by anterior pituitary gland

113
Q

Oestrogen

A

• stimulates secretion of LH
• stimulates the uterus to produce a new endometrium
• inhibits FSH
• secreted by the ovary

114
Q

Progesterone

A

• maintains the endometrium
• stimulates oestrogen secretion
• inhibits FSH and LH
• secreted by the corpus luteum

115
Q

Amnion

A

A membrane which is derived from the inner cell mass of the blastocyst
The foetus is enclosed within the amnion
Around week 4-5, the amniotic fluid is produced bu the mother
About 4 months - foetus contributes urine to it

116
Q

Function of amniotic fluid

A

• shock absorber - protection
• maintains the foetus’ temperature
• provides lubrication
• allows movement so muscles and bones function before birth

117
Q

Hormones during pregnancy

A

• Human chorionic gonadotropin is secreted by the embryo maintains the corpus luteum for the first 16 weeks and so endometrium is maintained
• placenta secretes high levels of oestrogen and progesterone and so FSH and LH are inhibited
• progesterone inhibits oxytocin
• oestrogen stimulates growth of uterus to accommodate growing foetus and stimulates the growth and development of mammary glands during pregnancy

118
Q

Hormones during birth

A

• oestrogen increases
• progesterone decreases - myometrium can now contract as oxytocin is released by the posterior pituitary gland and works by positive feedback
• prolactin is secreted by the anterior lobe of the pituitary gland during and after birth to stimulate the production of milk by mammary glands

119
Q

Aneuploidy

A

Loss or gain of single chromosome

120
Q

Polyploidy

A

Changes in number of whole sets of chromosomes

121
Q

What is the function of hCG in pregnancy

A

Maintain the corpus luteum

122
Q

How did the results of the human genome project made the use of gene editing possible

A

• identification of the position of all genes
• base sequence of normal genes found

123
Q

Double fertilisation in plants

A

• first male gamete fuses with female gamete to produce a zygote
• second male gamete fuses with the polar nucleus to form the triploid endosperm nucleus

Wjec A Level Biology (13 decks)

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