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EDEXCEL BIOLOGY > test 2 > Flashcards

test 2 Flashcards

1
Q

How are sperm cells specialised for their function?

A

1 - nucleus containing haploid chromosomes
2 - tightly packed mitochondria to provide ATP for movement of tail
3 - flagellum propels sperm
4 - microtubules keep sperm in suspension to move tail
5 - acrosome stores enzymes to digest zona pellucida

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2
Q

Describe the structure of an egg cell

A

1 - follicle cells release chem for acrosome reaction
2 - zona pellucida: glycoprotein for sperm to bind
3 - cortical granules
4 - lipid droplets: food store for embryo

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3
Q

What is the role of the cortical granules?

A

lysosome which releases enzymes to thicken zona pellucida and prevent further entry of sperm

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4
Q

Describe the stages of fertilisation

A

1 - Follicle cell releases chemical which triggers acrosome reaction
2 - Acrosome membrane fuses with front of sperm cell membrane and digestive enzymes released
3 - Enzymes digest zona pellucida
4 - Sperm membrane fuses with ovum membrane & nucleus enters ovum
5 - Cortical reaction: zona pellucida thickens to prevent entry of other sperm
6 - Egg and sperm nuclei fuse - diploid zygote

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5
Q

How does meiosis create genetic variation?

A

Crossing over of chromatids: same genes but different alleles
Independent assortment: different combo of maternal and paternal chromosomes

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6
Q

What is a gene locus?

A

Location of genes on a chromosome

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7
Q

What is gene linkage?

A

Genes with loci on the same chromosome so they aren’t inherited separately

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8
Q

The closer the loci of 2 genes…

A

The more closely they’re linked and less likely to be separated by crossing over

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9
Q

How do cells specialise?

A

Gene activated by stimulus
mRNA transcribed from active gene and translated into proteins
Protein determines structure and function of cell

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10
Q

How do transcription factors control gene expression in eukaryotes?

A

Methylation of DNA prevents transcription by stopping RNA polymerase binding
Histone modification - acetylation makes chromatin less condensed so RNA polymerase can bind

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11
Q

How can gene expression be controlled?

A

Rate of transcription of genes
Transcription factors
Activators & repressors

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12
Q

What is an operon?

A

Section of DNA containing promoter and operator

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13
Q

What happens when lactose is present?

A

Binds to repressor, changing its shape so it can’t bind to the promoter, B galactosidase expressed

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14
Q

What happens when lactose is absent?

A

Lac repressor binds to operator site and stops transcription as RNA polymerase can’t bind to promoter

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15
Q

What is biodiversity?

A

Number of different species and genetic variation within species

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16
Q

Define ecosystem

A

A self-sustaining life-supporting environment with biotic and abiotic factors

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17
Q

What is species evenness?

A

when species have similar abundances, no dominant species

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18
Q

How is genetic variation measured?

A
  1. DNA sequenced to determine bases and alleles
  2. DNA copied using PCR and cut with restriction enzymes
  3. fragments separated by gel electrophoresis to create a banding pattern
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19
Q

What does 2 bands in gel electrophoresis mean?

A

heterozygous as there’s a band for each allele

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20
Q

What is the heterozygosity index?

A

number of heterozygotes / number of individuals in a population

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21
Q

Why is a large heterozygosity index good?

A

more heterozygous a population, the larger the gene pool

increased chance of survival

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22
Q

Why is inbreeding bad?

A

heterozygosity lost, smaller gene pool
decreased chance of survival
recessive alleles have harmful effects (inbreeding depression)

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23
Q

How is maltose formed?

A

2 alpha glucose in condensation

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24
Q

How is sucrose formed?

A

Alpha glucose and alpha fructose (1-2) glycosidic bond

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25
Q

How is lactose formed?

A

Beta galactose and alpha glucose B(1-4) glycosidic

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26
Q

Function of maltose

A

Respiratory substrate, germinating seeds

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27
Q

Function of sucrose

A

Transporting energy in plants

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28
Q

Function of lactose

A

mammalian milk

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29
Q

How is the structure of starch related to its function?

A

Amylopectin large chain of glucose units: available for respiration
Amylose helix coiled: compact, lots of glucose in small space
Amylopectin is branched and compact: lots of glucose for resp
Large so it’s insoluble

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30
Q

How is the structure of glycogen related to its function?

A

Branched: easily hydrolysed do glucose released quickly
Compact, stores lots of glucose
Large, so it’s insoluble

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31
Q

Describe the structure of cellulose

A

Alpha glucose and beta

Unbranched straight chains align parallel to each other forming microfibrils (H bond)

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32
Q

What are some natural causes of rising temperatures?

A
  • variations in solar activity
  • fluctuations in ocean currents
  • volcanic eruptions
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33
Q

How do ice cores help determine temperature?

A

measurement of O-18 and O-16

warmer climates have more O-18 because it is preferred in precipitation and evaporates

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34
Q

What are the conditions in peat bogs?

A

acidic, cool, anaerobic

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35
Q

Why do anaerobic conditions reduce decompositions?

A

no oxygen so decomposing bacteria can’t respire so die
digestive enzymes not present
acidic pH reduces enzyme action

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36
Q

Why might peat bogs not provide any evidence sometimes?

A

layers destroyed or mixed

37
Q

Why is pollen in peat bogs useful? (4)

A

large amounts
resistant to decomposition
distinct pollen for diff species
each species grows best in particular climate

38
Q

How are insect records taken from peat bogs and why are they more useful?

A

exoskeleton preserved in bogs

populations respond faster to climate change so more accurate

39
Q

Is the spring growth dark or light? Why?

A

light because it’s wet and warm so wider xylem vessels

40
Q

Is summer growth dark or light? Why?

A

dark because it’s warmer and dry so less growth and narrow xylem

41
Q

What is the atmosphere?

A

a layer of gases surrounding a planet

42
Q

How does the atmosphere sustain life? (3)

A

contains O2 for respiration, CO2 for PS
ozone layer absorbs UV light, reducing genetic damage
maintains stable average temp, sustaining life

43
Q

How does the atmosphere maintain a stable temperature?

A

greenhouse effect

44
Q

Describe the greenhouse effect

A
  1. Short wavelength solar radiation passes through atmosphere
  2. Some radiation absorbed, warming the Earth
  3. Some longer IR radiation reflected off the Earth’s surface
  4. Longer wavelength IR absorbed by greenhouse gases, increasing the Earth’s temperature
45
Q

Which greenhouse gas has the biggest effect on GHE?

A

water vapour because it has a high specific heat capacity and can absorb the most heat energy

46
Q

What is global warming potential (GWP)?

A

a relative measure of how much heat a green house gas traps in the atmosphere

47
Q

What is global warming?

A

enhanced greenhouse effect due to an increased level of greenhouse gases

48
Q

What does two data sets from different locations confirm?

A

that the trend is global

49
Q

Why are there CO2 fluctuations?

A

photosynthesis high in summer and low in winter

summer: PS > R
winter: R > PS

50
Q

Why are CO2 levels increasing? (2)

A

increase in fossil fuel in combustion so growing energy demand
deforestation (less PS)

51
Q

What are the sources of methane? (4)

A

anaerobic bacteria in marshes and rice paddies
anaerobic bacteria in guts of ruminants
decomposition of organic material
leakage from gas pipes

52
Q

Why are methane levels increasing? (3)

A

increase in rice paddy fields due to demand for food
increase in ruminant population due to demand for food
increase in number of landfill sites

53
Q

What are the sources of nitrous oxide? (2)

A

combustion of fossil fuels

denitrifying bacteria acting on nitrates

54
Q

Why are nitrous oxide levels increasing? (3)

A

increase in fossil fuel combustion
increased use of nitrate fertilisers
increased cultivation of soil

55
Q

Why is climate change science controversial? (5)

A 
science cannot prove theories
alternative interpretations exist
knowledge about climate is incomplete
available data has limitations
interpretation bias
56
Q

What is a scientific theory?

A

a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence and upon which predictions can be made

57
Q

What are some limitations with data?

A

Not a long data set
Only from 1 country
Other factors responsible
Validity of experiment - how was it measured?

58
Q

What is extrapolation?

A

an estimate outside the recorded or observed range

59
Q

What assumptions are made when extrapolating?

A
  • enough data to establish a trend

- present trend continues

60
Q

What factors need to be taken into account to predict CO2 concentration? (5)

A
  • price of fossil fuel
  • Kyoto protocol
  • clean technology
  • amount of PS
  • increase in population
61
Q

What are climate models?

A

quantitative methods to simulate the interactions of the different factors to project future climate

62
Q

What are the limitations of climate models? (5)

A
  • limited data
  • limited knowledge on how climate works
  • limiting computing resources
  • not all factors considered
  • changing factors
63
Q

How are flora and fauna adapting to climate change?

A
  • changes in distribution
  • changes in development
  • changes in life cycle
64
Q

How is distribution of species changing? Why?

A
  • species migrating north
  • loss of habitats and food sources (not ideal conditions)
  • competition with aliens species and changes in dominant species
65
Q

What happens to rate of reaction when temperature increases?

A
  • increases (doubles for every 10C increase)

- more collisions of substrate and enzyme due to higher KE

66
Q

Why does rate of reaction decrease when temperature is increased too much?

A
  • secondary and tertiary bonds break due to high vibration of molecules
  • enzyme denatures, active site changes shape, no binding of substrate
67
Q

What happens when rainfall patterns change?

A
  • affects development and life cycles of organisms (plants remain dormant for longer)
  • affects distribution of species: more desert areas
68
Q

Describe the structure and function of smooth muscle

A
  • non striated
  • spindle shaped
  • uninuclear fibres
  • involuntary
  • in walls of internal organs
69
Q

Describe the structure and function of cardiac muscle

A
  • striated
  • branched
  • uninuclear fibres
  • involuntary
  • walls of the heart
70
Q

Describe the structure and function of skeletal muscle

A
  • striated
  • tubular
  • multinuclear fibres (cells)
  • voluntary
  • attached to skeleton
71
Q

What is a tendon?

A

joins muscles to bones

  • white fibrous tissue
  • bundles of collagen fibres
  • inelastic
72
Q

What is cartilage?

A

tissue at the ends of bones, made of chondrocytes and collagen, to prevent bone erosion

  • elastic
  • shock absorber
73
Q

How do muscles allow movement?

A

antagonist pairs which work in opposite directions:

  • flexor (reduces angle)
  • extensor (straightening)
74
Q

Describe the structure of a section of skeletal muscle

A

bundles of muscle fibres with myocytes (single muscle cells)

75
Q

Describe the structure of a myocyte

A
  • multi-nucleate
  • made up of contractile myofibrils
  • sarcolemma, sarcoplasm, sarcoplasmic reticulum
  • sarcosomes (mitochondria) for ATP
76
Q

What are myofibrils?

A

bundles of myofilaments, which are repeated chains of sarcomeres

77
Q

What are A bands?

A

dark bands contain thick myosin and overlapping thin actin

78
Q

What are I bands?

A

light bands containing only thin actin filaments

79
Q

What is the Z line?

A

sarcomeres are joined here

80
Q

What is the M line?

A

middle of the myosin filaments

81
Q

What does the H zone contain?

A

only thick myosin filaments

82
Q

What happens to the I band in contraction?

A

gets shorter

83
Q

What happens to the A band in muscle contraction?

A

stays the same

84
Q

What happens to the H zone in contraction?

A

gets shorter

85
Q

What happens when muscles are relaxed?

A
  • no Ca2+ so tropomyosin blocks the myosin binding site on actin
  • myofilaments can’t slide past each other as heads can’t bind
86
Q

How is muscle contraction triggered?

A
  • nerve impulse reaches axon terminals at neuromuscular junction
  • depolarises sarcolemma and spreads to sarcoplasm
  • neurotransmitter released and binds to receptors on muscle cells
  • Ca2+ released from sarcoplasmic reticulum
87
Q

How do muscles contract?

A

1 - Ca2+ binds to troponin and pulls tropomyosin away from binding site
2 - Myosin head (ADP + Pi) attaches to actin, forming cross bridge
3 - Pi released, causing power stroke: myosin pulls on actin
4 - ADP released
5 - ATP binds to myosin head and cross-bridge detaches
6 - Myosin ATPase hydrolyses ATP to ADP + Pi so it has energy

88
Q

What is sex linkage?

A

Genes that are on the sex chromosome and inherited with the sex chromosome

EDEXCEL BIOLOGY (14 decks)

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