test 2 Flashcards
How are sperm cells specialised for their function?
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
Describe the structure of an egg cell
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
What is the role of the cortical granules?
lysosome which releases enzymes to thicken zona pellucida and prevent further entry of sperm
Describe the stages of fertilisation
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
How does meiosis create genetic variation?
Crossing over of chromatids: same genes but different alleles
Independent assortment: different combo of maternal and paternal chromosomes
What is a gene locus?
Location of genes on a chromosome
What is gene linkage?
Genes with loci on the same chromosome so they aren’t inherited separately
The closer the loci of 2 genes…
The more closely they’re linked and less likely to be separated by crossing over
How do cells specialise?
Gene activated by stimulus
mRNA transcribed from active gene and translated into proteins
Protein determines structure and function of cell
How do transcription factors control gene expression in eukaryotes?
Methylation of DNA prevents transcription by stopping RNA polymerase binding
Histone modification - acetylation makes chromatin less condensed so RNA polymerase can bind
How can gene expression be controlled?
Rate of transcription of genes
Transcription factors
Activators & repressors
What is an operon?
Section of DNA containing promoter and operator
What happens when lactose is present?
Binds to repressor, changing its shape so it can’t bind to the promoter, B galactosidase expressed
What happens when lactose is absent?
Lac repressor binds to operator site and stops transcription as RNA polymerase can’t bind to promoter
What is biodiversity?
Number of different species and genetic variation within species
Define ecosystem
A self-sustaining life-supporting environment with biotic and abiotic factors
What is species evenness?
when species have similar abundances, no dominant species
How is genetic variation measured?
- DNA sequenced to determine bases and alleles
- DNA copied using PCR and cut with restriction enzymes
- fragments separated by gel electrophoresis to create a banding pattern
What does 2 bands in gel electrophoresis mean?
heterozygous as there’s a band for each allele
What is the heterozygosity index?
number of heterozygotes / number of individuals in a population
Why is a large heterozygosity index good?
more heterozygous a population, the larger the gene pool
increased chance of survival
Why is inbreeding bad?
heterozygosity lost, smaller gene pool
decreased chance of survival
recessive alleles have harmful effects (inbreeding depression)
How is maltose formed?
2 alpha glucose in condensation
How is sucrose formed?
Alpha glucose and alpha fructose (1-2) glycosidic bond
How is lactose formed?
Beta galactose and alpha glucose B(1-4) glycosidic
Function of maltose
Respiratory substrate, germinating seeds
Function of sucrose
Transporting energy in plants
Function of lactose
mammalian milk
How is the structure of starch related to its function?
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
How is the structure of glycogen related to its function?
Branched: easily hydrolysed do glucose released quickly
Compact, stores lots of glucose
Large, so it’s insoluble
Describe the structure of cellulose
Alpha glucose and beta
Unbranched straight chains align parallel to each other forming microfibrils (H bond)
What are some natural causes of rising temperatures?
- variations in solar activity
- fluctuations in ocean currents
- volcanic eruptions
How do ice cores help determine temperature?
measurement of O-18 and O-16
warmer climates have more O-18 because it is preferred in precipitation and evaporates
What are the conditions in peat bogs?
acidic, cool, anaerobic
Why do anaerobic conditions reduce decompositions?
no oxygen so decomposing bacteria can’t respire so die
digestive enzymes not present
acidic pH reduces enzyme action
Why might peat bogs not provide any evidence sometimes?
layers destroyed or mixed
Why is pollen in peat bogs useful? (4)
large amounts
resistant to decomposition
distinct pollen for diff species
each species grows best in particular climate
How are insect records taken from peat bogs and why are they more useful?
exoskeleton preserved in bogs
populations respond faster to climate change so more accurate
Is the spring growth dark or light? Why?
light because it’s wet and warm so wider xylem vessels
Is summer growth dark or light? Why?
dark because it’s warmer and dry so less growth and narrow xylem
What is the atmosphere?
a layer of gases surrounding a planet
How does the atmosphere sustain life? (3)
contains O2 for respiration, CO2 for PS
ozone layer absorbs UV light, reducing genetic damage
maintains stable average temp, sustaining life
How does the atmosphere maintain a stable temperature?
greenhouse effect
Describe the greenhouse effect
- Short wavelength solar radiation passes through atmosphere
- Some radiation absorbed, warming the Earth
- Some longer IR radiation reflected off the Earth’s surface
- Longer wavelength IR absorbed by greenhouse gases, increasing the Earth’s temperature
Which greenhouse gas has the biggest effect on GHE?
water vapour because it has a high specific heat capacity and can absorb the most heat energy
What is global warming potential (GWP)?
a relative measure of how much heat a green house gas traps in the atmosphere
What is global warming?
enhanced greenhouse effect due to an increased level of greenhouse gases
What does two data sets from different locations confirm?
that the trend is global
Why are there CO2 fluctuations?
photosynthesis high in summer and low in winter
summer: PS > R
winter: R > PS
Why are CO2 levels increasing? (2)
increase in fossil fuel in combustion so growing energy demand
deforestation (less PS)
What are the sources of methane? (4)
anaerobic bacteria in marshes and rice paddies
anaerobic bacteria in guts of ruminants
decomposition of organic material
leakage from gas pipes
Why are methane levels increasing? (3)
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
What are the sources of nitrous oxide? (2)
combustion of fossil fuels
denitrifying bacteria acting on nitrates
Why are nitrous oxide levels increasing? (3)
increase in fossil fuel combustion
increased use of nitrate fertilisers
increased cultivation of soil
Why is climate change science controversial? (5)
science cannot prove theories alternative interpretations exist knowledge about climate is incomplete available data has limitations interpretation bias
What is a scientific theory?
a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence and upon which predictions can be made
What are some limitations with data?
Not a long data set
Only from 1 country
Other factors responsible
Validity of experiment - how was it measured?
What is extrapolation?
an estimate outside the recorded or observed range
What assumptions are made when extrapolating?
- enough data to establish a trend
- present trend continues
What factors need to be taken into account to predict CO2 concentration? (5)
- price of fossil fuel
- Kyoto protocol
- clean technology
- amount of PS
- increase in population
What are climate models?
quantitative methods to simulate the interactions of the different factors to project future climate
What are the limitations of climate models? (5)
- limited data
- limited knowledge on how climate works
- limiting computing resources
- not all factors considered
- changing factors
How are flora and fauna adapting to climate change?
- changes in distribution
- changes in development
- changes in life cycle
How is distribution of species changing? Why?
- species migrating north
- loss of habitats and food sources (not ideal conditions)
- competition with aliens species and changes in dominant species
What happens to rate of reaction when temperature increases?
- increases (doubles for every 10C increase)
- more collisions of substrate and enzyme due to higher KE
Why does rate of reaction decrease when temperature is increased too much?
- secondary and tertiary bonds break due to high vibration of molecules
- enzyme denatures, active site changes shape, no binding of substrate
What happens when rainfall patterns change?
- affects development and life cycles of organisms (plants remain dormant for longer)
- affects distribution of species: more desert areas
Describe the structure and function of smooth muscle
- non striated
- spindle shaped
- uninuclear fibres
- involuntary
- in walls of internal organs
Describe the structure and function of cardiac muscle
- striated
- branched
- uninuclear fibres
- involuntary
- walls of the heart
Describe the structure and function of skeletal muscle
- striated
- tubular
- multinuclear fibres (cells)
- voluntary
- attached to skeleton
What is a tendon?
joins muscles to bones
- white fibrous tissue
- bundles of collagen fibres
- inelastic
What is cartilage?
tissue at the ends of bones, made of chondrocytes and collagen, to prevent bone erosion
- elastic
- shock absorber
How do muscles allow movement?
antagonist pairs which work in opposite directions:
- flexor (reduces angle)
- extensor (straightening)
Describe the structure of a section of skeletal muscle
bundles of muscle fibres with myocytes (single muscle cells)
Describe the structure of a myocyte
- multi-nucleate
- made up of contractile myofibrils
- sarcolemma, sarcoplasm, sarcoplasmic reticulum
- sarcosomes (mitochondria) for ATP
What are myofibrils?
bundles of myofilaments, which are repeated chains of sarcomeres
What are A bands?
dark bands contain thick myosin and overlapping thin actin
What are I bands?
light bands containing only thin actin filaments
What is the Z line?
sarcomeres are joined here
What is the M line?
middle of the myosin filaments
What does the H zone contain?
only thick myosin filaments
What happens to the I band in contraction?
gets shorter
What happens to the A band in muscle contraction?
stays the same
What happens to the H zone in contraction?
gets shorter
What happens when muscles are relaxed?
- no Ca2+ so tropomyosin blocks the myosin binding site on actin
- myofilaments can’t slide past each other as heads can’t bind
How is muscle contraction triggered?
- 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
How do muscles contract?
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
What is sex linkage?
Genes that are on the sex chromosome and inherited with the sex chromosome