SB6, SB7, SB8, SB9 Biology (paper 2) 📍 Flashcards
Chloroplast definition
site of photosynthesis
organelles in a plant cell
cell wall, vacuole, chloroplast, mitochondria, ribosomes, nucleus, cell membrane, cytoplasm
Reagent used to test for starch
Iodine
What are the plant organs
Stem, root and leaves
what are the tissue layers in a leaf?
• Cuticle
• Upper epidermis
• Palisade mesophyll
• Spongy mesophyll
• Lower epidermis
What tissue layer does photosynthesis occur in?
Palisade mesophyll
What is the cuticle?
• A waxy waterproof, transparent layer
• Reduces water loss during evaporation
• Acts as a layer of protection
What is the upper epidermis?
Transparent layer in order to allow light to be absorbed
Palisade mesophyll tissue layer
Large number of palisade cells are found here to maximise rate of protein synthesis
Adaptation of the spongy mesophyll
Contains air spaces to maximise surface area and increase gas exchange
Function of the guard cells
• Controls the opening and closing of the stomata
• Allows gases to diffuse in or out
• Also allows water vapour to leave
What are the 2 transport vessels in a plant?
Xylem and phloem
Function of xylem
Transports water and dissolved mineral ions
Function of phloem
Transports sucrose (sugar) and amino acids
Endothermic reaction
Chemical reaction where heat is absorbed
Function of roots
Absorb water and nutrients from the soil
Photosynthesis definition
the process by which plants convert sunlight, water, and carbon dioxide into oxygen and glucose.
Autotroph meaning
Plants can make complex molecules (glucose) from simple molecules (co2 and water)
Producer meaning
Organisms (plants) that are able to make their own food and therefore are at the start of all food chains
Word equation for photosynthesis
Carbon dioxide + Water
—> Glucose + Oxygen
Function of glucose in plants
• Produces starch for storage
• Helps with respiration
• Synthesises lipids to provide seeds with energy
• Form cellulose to make cell walls
Function of oxygen in plants
Helps with respiration or it diffuses out
Diffusion definition
Movement of particles from high to low concentration
What is a limiting factor?
Factor that slows down rate of a process (eg photosynthesis)
3 factors that can affect rate of photosynthesis
Temperature, C02 concentration and light intensity
Denatured meaning
When the active site of an enzyme loses its shape and is no longer complementary to the substrate
Pigment found in chloroplasts
Chlorophyll
Factors that affect amount of chloroplasts
Amount of leaves, amount of nutrients, diseases
Equipment that can be used to measure light intensity
Light meter
What is light measured in?
Lux
Why is there a higher concentration of carbon dioxide at night in plants?
there’s a higher rate of respiration as it doesn’t photosynthesise. This produces more carbon dioxide.
How does a high temperature affect the rate of photosynthesis?
Enzymes become denatured [state meaning]
How do low temperatures affect the rate of photosynthesis?
Less kinetic energy is present therefore less collisions occurs between molecules meaning that less reactions happen
What’s the optimum temperature for photosynthesis
25 degrees Celsius
How do guard cells control the opening and closing of the stomata?
When the plant has a sufficient amount of water, the guard cells take in the water and swell (turgid) causing the stomata to open to allow gas exchange.
Inverse square law calculation
1/d² - Light intensity is inversely proportional to distance
Method to measure volume of gas released in photosynthesis
[might come soon]
adaptations of root hair cells
• Absorbs water (by osmosis) and mineral ions (active transport)
• Has extensions to increase its surface area and increase absorption
What organelle do roots hair cells not have and why?
Chloroplast because they are underground and cannot absorb light for photosynthesis
Active transport meaning
An energy requiring process where substances are moved across a cell membrane against their concentration gradient
Osmosis meaning
Movement of water molecules across a semi permeable membrane from a high concentration to low concentration
Direction of flow in xylem
Upwards and unidirectional
Location of xylem in relation to phloem in a vascular bundle
Xylem is on the inside whereas the Phloem is on the outside
function of sucrose
transports amino acids
How is water transported in a plant
Absorbed through osmosis in the root and then up the xylem through transpiration
Define transpiration
The pull of water from the root to the leaves to replace the evaporated water
Monomer of sucrose
Glucose
Function of sodium hydrogen carbonate
Provides plant with Co2 when added to water to support with photosynthesis
Function of protease
Breaks down proteins in cell membrane
adaptations of the xylem
• No end walls (to form hollow tubes for water to be drawn)
• Contains no cytoplasm (for free passage of water)
• Lignin thickens the outer walls (to strengthen tubes)
Adaptations of the phloem
• Cells have few organelles (to aid the flow of sugars and amino acids)
• Cells are joined end to end by sieve plates (forming tubes to allow translocation)
• Small pores in end walls let substances through
Companion cell function
Supports the transport of sugars and amino acids from the leaves to phloem by providing energy
Translocation meaning
Active transport of sugars from leaves into phloem
Direction of flow in phloem
Bidirectional
Xerophytic plant meaning
Plant adapted to survive in extreme conditions
Examples of xerophytic plants
Cacti and Marram grass
Adaptations of xerophytic plants
• stem stores water
• stomata opens at night (because it’s cooler and reduces water loss)
• hairs on stem (to trap water vapour)
• waxy, thick cuticle
Structural adaptations of marram grass in a hot, windy and dry environment
Its leaves roll up to reduce exposure to wind (minimising water loss) • Thick cuticle to reduce water loss • Hairs on inner surface of the leaf (trapping air to reduce water loss)
Plant adaptations of marram grass in a hot, windy and dry environment
• Long thin leaves to reduce air resistance • strong root structure to prevent being uprooted • flexible to avoid breaking (in windy conditions)
Pathway of water in a plant
Root hair cells -> Root cortex cells -> Xylem -> Leaf mesophyll cells
Why does the stomata open during the day?
• Higher light intensity allows for gas exchange (photosynthesis) • which allows water vapour to leave during transpiration
Why does the stomata close during the night?
To conserve water as the rate of transpiration is reduced (photosynthesis can’t occur)
Turgid meaning
Swollen
What happens when water leaves the guard cells?
The guard cells become flaccid • Stomata also closes
Cohesion meaning
When water molecules stick together
Function of transpiration
• Transports mineral ions • Provides water to keep cells turgid for photosynthesis • Keeps leaves cool (water evaporates)
How is the flow of water continuous
Due to the cohesion of water it creates a continuous unbroken column
Factors that affect the rate of transpiration
• Temperature • Light intensity • Air movement • Humidity
How does temperature affect transpiration?
• A higher temperature increases kinetic energy of water molecules • This makes transpiration through evaporation faster
How does light intensity affect transpiration?
• A higher light intensity would increase the rate of photosynthesis by opening more stomata for co2 to diffuse in • This allows more water to evaporate
How does air movement affect transpiration?
• Moving air removes water vapour in the air and increases the concentration gradient • Allows evaporation to happen faster
How does humidity affect transpiration?
• A lot of water vapour in the air reduces the water concentration gradient • This decreases the rate of evaporation
Potometer meaning
Apparatus used to measure the rate of transpiration
Why is the shoot (upper part of plant) cut under water?
To prevent air entering the xylem
Why are the leaves of the shoot dried?
To remove any excess water
Equation to work out the rate of transpiration
Rate = Distance moved by air bubble (m) / Time (min)
How can we reduce leaking in a potometer?
Assemble equipment underwater
Source meaning
Where the products are made
Sink meaning
Where the products are stored/ used
Phototropism meaning
Response to light in a directional movement
Geotropism meaning
Response to gravity in a directional movement
What tropic responses do shoots have?
Shoots have a positive phototropism and a negative geotropism
What tropic responses do roots have?
Roots have a negative phototropism and a positive geotropism
What are auxins?
Growth regulators synthesised in the tips of shoots and roots
How are auxins distributed in phototropism?
• Auxins are synthesised in the tips of shoots • Auxins diffuse to the shaded side in response to light • This increases the concentration of auxins in the shaded side • Therefore cells in the shaded side elongate at a faster rate • Causing the shoot to bend towards the light
What are auxins similar to?
Hormones
How are auxins distributed in geotropism?
Auxins are synthesised in the tips of roots • Auxins diffuse to the lower side • This increases the concentration of auxins in the lower side and inhibits cell elongation • Causing the cells at the top of the root to elongate at a faster rate (in response to gravity)
What are plant hormones used by farmers for?
To obtain larger yields
What are three plant hormones?
Auxins, ethenes and gibberellins
How are auxins used commercially?
They are used as weed killers to maximise yield • Sold as rooting powders to encourage rapid development of roots
What is the commercial use of ethene?
It controls the ripening of fruit
How are gibberellins used commercially?
They end seed dormancy: promoting seed germination • Produce seedless fruit • Increase fruit size
Seed dormancy definition
When seeds are unable to germinate even under ideal growing conditions
Concentration gradient meaning
A difference between two concentrations
Dependent variable meaning
The variable you measure
Independent variable meaning
The variable you change
The rate of photosynthesis is directly proportional to what?
Light intensity
[SB8]
What substances are exchanged in and out of organisms?
• Oxygen
• Carbon dioxide (waste)
• Water
• Dissolved food molecules (eg glucose)
• Mineral ions
• Urea (waste)
What are the transport processes?
• Diffusion
• Osmosis
• Active transport
Why do multi cellular organisms need exchange surfaces?
• The distance between the surface and its centre is long (long diffusion distance)
• They have a small surface area in comparison to their volumes (SA:V)
• The transport processes cannot happen sufficiently without them
How is villi adapted for absorption?
• It’s the folded membrane of small intestines
• This increases SA and absorption rate of digested food
Transport system in animals
• The blood and circulatory system
Exchange surfaces in animals
• Lungs and alveoli for gas exchange
• Small intestines and villi for absorption of digested food
Transport systems in plants
• Xylem (moves water and mineral ions from roots to shoots)
• Phloem (moves sugars and amino acids to where necessary)
Exchange surfaces in plants
• Roots and hairs (mineral ions and water are absorbed)
• Leaves (stomata - gas exchange)
Factors affecting the rate of diffusion
• Surface area
• Concentration gradient
• Diffusion distance
• Temperature
How does surface area affect the rate of diffusion?
• The bigger a cell the smaller its surface area to volume ratio
• This slows down the rate of diffusion
How does diffusion distance affect the rate of diffusion?
• The smaller the distance molecules travel, the faster the transport
• Eg blood capillaries and alveoli have walls one cell thick
• This increases the rate of diffusion
How does the concentration gradient affect the rate of diffusion?
• The greater the difference in concentration the faster the movement
• Therefore more random collisions will occur against the membrane
How does temperature affect the diffusion rate?
• The higher the temperature, the faster molecules move as they have more kinetic energy
• This results in more collisions against the cell membrane and a faster rate of movement across it
What is Fick’s law?
Diffusion rate ∝ (surface area x concentration gradient) / diffusion distance
• The rate of diffusion is directly proportional to the surface area and concentration gradient
• But inversely proportional to the thickness of the membrane (diffusion distance)
Organelle where exchange of substances occur
Cell membrane
What type of reaction is respiration?
An exothermic reaction
Products formed when lipids are digested
Fatty acids and glycerol
Why do organisms need energy?
• Chemical reactions to build large molecules from smaller ones
• Muscle contraction to allow movement
• Keeping warm (to maintain a constant temperature for optimum enzyme activity)
Definition of aerobic respiration
The chemical reaction in cells that uses oxygen to completely break down nutrient molecules to release energy
Aerobic respiration word equation
Glucose + Oxygen —> Carbon dioxide + Water
Where does aerobic respiration occur in a cell?
Mitochondria
Products in respiration
• Carbon dioxide
• Water
• Useful energy
Anaerobic respiration definition
Chemical reaction in cells that partially breaks down nutrient molecules to release energy without using oxygen
Differences between aerobic and anaerobic respiration
• Aerobic respiration requires oxygen whilst anaerobic doesn’t
• Glucose is only completely broken down aerobically
• Aerobic respiration releases larger amounts of energy
Chemical equation for aerobic respiration
C6H12O6 + 6O2 —> 6CO2 + 6H2O
(+ energy/ATP)
What is ATP?
• Short term energy store in all cells
• Universal energy carrier
Where does anaerobic respiration take place?
Muscle cells during vigorous exercise
Why do our bodies use anaerobic respiration?
• When we exercise at high intensities our muscles have a higher demand for energy
• Therefore oxygen is likely to run out and when it does glucose is broken down without it, producing lactic acid instead
• Glucose has not been fully broken down so there’s still energy stored in the bonds of lactic acid molecules
• Which results in less energy being released
Word equation for anaerobic respiration in animals
Glucose —> Lactic acid
Effect of lactic acid buildup
It lowers the pH of the muscle tissue as it makes the blood more acidic
Oxygen debt
The amount of oxygen required to break down the lactic acid that has built up
Which organisms other than animals respire anaerobically?
• Plants
• Yeast (fungi)
What is fermentation?
Anaerobic respiration in yeast cells
What is the economic importance of fermentation?
• It’s used in the manufacturing of bread
(CO2 helps the dough to rise)
• It’s used in brewing
(ethanol produced makes beer)
Word equation for anaerobic respiration in plants and fungi
Glucose —> Alcohol + Carbon dioxide
How is iodine used to test for starch?
It changes its colour to blue/black
Purpose of soda lime in the rate of respiration practical
It absorbs any co2 to prevent it affecting the measuring of oxygen
Purpose of cotton wool in the rate of respiration practical
It protects us and the organisms used from the soda lime because it’s harmful
Purpose of inserting a bung with the capillary tube
• Allows us to accurately measure how much oxygen is used up
• No air is lost/gained from surrounding area
Purpose of setting up a control tube
The tube will have no organisms in it to ensure results are only due to respiration
Why do we time for 5 minutes after marking the position of the coloured liquid?
• Time is the control variable and prevents results from being affected
Why do we measure the distance the liquid has travelled in the rate of respiration practical?
• It is the dependent variable
• It allows us to see how much oxygen has been consumed
Why do we repeat the rate of respiration practical at different temperatures?
• Independent variable
• Range of temperatures would help identify the effect it has on respiration
What are the 4 blood components?
• Red blood cells
• White blood cells
• Plasma
• Platelets
What are the 3 types of blood vessels?
• Arteries
• Veins
• Capillaries
What is a eukaryotic cell?
A cell that contains genetic information within a nucleus
Adaptations of the alveoli
• They are small sacs that increase the SA:V ratio
• They have thin single layers of cells to minimise diffusion distance
• They have ventilation to maintain high levels of O2 entering lungs and low levels of CO2
• They have a good blood supply to ensure a constant supply of blood high in CO2 and low in O2
• They have a layer of moisture on the surface to dissolve gases which supports diffusion
What does ventilation and a good blood supply do for alveoli?
It maintains the concentration gradient
What is blood?
The liquid that transports important substances around the body
(eg oxygen and glucose)
Functions of the blood
• Helps defend the body against pathogens
• Helps control body temperature
• Helps to maintain the pH of cells
Function of plasma
• Carries red and white blood cells and platelets
• Carries dissolved substances eg glucose and oxygen
What colour is plasma?
Yellow
Why is the blood red?
Due to the haemoglobin in red blood cells
What is haemoglobin?
The pigment in red blood cells that binds to oxygen and transports it
Function of red blood cells
They carry oxygen from the air in our lungs to our respiring cells
Function of white blood cells
• Form part of the immune system (fights against infection)
• Lymphocytes produce antibodies
• Phagocytes engulf and digest pathogens
What are platelets?
Small fragments of cells without a nucleus and are involved in the clotting of blood
Function of platelets
• Helps with the clotting of blood
• Clotting forms a network of fibres that trap more platelets and red blood cells to form a scab
• This protects the new skin as it grows underneath
• This also prevents microorganisms from entering
Adaptations of red blood cells
• Are biconcave disks which increases their SA:V ratio and also diffusion
• Are packed with haemoglobin which binds to O2
• Have no nucleus which allows more space for haemoglobin
(• Haemoglobin contains an atom of iron which gives the pigment its red colour (is brightest when lots of oxygen is bound to it))
Anaemia meaning
Not having enough red blood cells in the body
Sickle cell anemia
• Consists of deformed red blood cells (loss of biconcave shape)
• Blood cells have a smaller volume and so cannot hold as much haemoglobin (and therefore cannot carry as much oxygen)
• Smaller surface area means that diffusion of oxygen is slower
• Shape can cause blood vessels to block which decreases blood flow
Impacts of having sickle cell anaemia
• Sufferers get breathless quickly and are often tired
• Less able to do exercise as muscles get tired quickly
Function of the arteries
• They carry oxygenated blood away from the heart and to the body
• Blood is under a high pressure
Adaptations of the arteries
• Have a thick layer of muscle and elastic fibres and also thick walls
• This helps it withstand the high pressure and be able to stretch
• Also have a narrow lumen to maintain high pressure
Function of the veins
• They carry deoxygenated blood away from organs towards the heart
• Blood is carried under low pressure
Adaptations of the veins
• They have a larger lumen and thin walls because blood is under low pressure
• Veins have valves to prevent blood flowing backwards due to gravity
How are the veins assisted with blood flow?
Muscles in the legs and arms help to push blood along the veins when moving
Function of the capillaries
They connect arteries and veins
Adaptations of the capillaries
• They are very narrow with thin walls one cell thick to minimise diffusion distance
• This increases the diffusion rate
• Also they have very narrow lumens that only allow 1 red blood cell to pass at a time
• This slows blood flow to increase the time oxygen diffuses into cells
• And maximises the diffusion of oxygen
How many chambers does the heart have and where are they found?
• 4
• Two upper chambers - left and right atrium
• Two lower chambers - left and right ventricles
What type of blood does the left side of heart carry?
Oxygenated blood
What type of blood does the right side of heart carry?
Deoxygenated blood
Function of the heart
Pumps blood around our body
Adaptations of the heart
• Made of 2 pumps
• The walls of our heart is mostly made of muscle
• A muscle wall (septum) separates the two sides of the heart
• Left ventricle is thicker which allows blood leaving it to be under high pressure as it pumps blood around the body
What is the coronary artery?
The blood vessel that supplies the heart with oxygen
What is the vena cava?
A vein that brings deoxygenated blood back to the heart
Describe the flow of deoxygenated blood through the heart (1)
• Blood flows through the vena cava then ➡️ right atrium
• Blood flows to ➡️ the right ventricle
• The tricuspid valve closes to prevent back flow
• The right ventricle contracts to force the deoxygenated blood into ➡️ the pulmonary artery
• Blood travels to ➡️ the lungs to pick up oxygen
Describe the flow of oxygenated blood through the heart (2)
• The newly oxygenated blood is returned to the heart by the pulmonary vein and flows into ➡️ the left atrium
• Blood flows into ➡️ the left ventricle and the bicuspid valve closes to prevent back flow
• The left ventricle pumps oxygenated blood around the body through ➡️ the aorta
Cardiac output definition
The volume of blood that is pumped by the heart per unit time
What impact does being fitter have on cardiac output?
Fitter people have higher cardiac outputs due to having thicker and stronger ventricular muscles in the heart
Heart rate meaning
The number of times a heart beats per minute
Stroke volume meaning
The volume of blood pumped out of the the left ventricle during one cardiac cycle
Calculation for cardiac output (cm³min-¹)
Heart rate (bpm) x Stroke volume (cm³)
What is the aorta?
Artery that transports oxygenated blood from the heart to the rest of the body
Tropism meaning
A plant’s response to stimulus
[[SB9]]
What is a population?
The number of individuals of a species in an area
What is a community?
The number of individuals of all species in an area
What is an ecosystem?
All the living organisms and the non-living components in an area
Biotic factor definition and examples
A living factor that affects an ecosystem
Eg:
• Food availability (plants)
• Predators (animals)
• Pathogens
• Competition
Abiotic factors definition and examples
A non-living factor that affects an ecosystem
Eg;
• soil pH and mineral content
• light intensity
• co2 levels for plants
• moisture levels
Interdependence meaning
When species rely on each other for survival
Resources plants and animals could compete for
• Food
• Space
• Water
• Mates
• Pollination
How could you improve an investigation?
• Use smaller intervals
Repeating experiment to:
• Calculate a mean
• Collect more data
• Identify anomalies
Examples of interactions that create interdependence in a community
• Parasitism
• Mutualism
What is mutualism?
A relationship between two species where both benefit
What is parasitism?
A relationship between two species where the parasite benefits but the host is harmed
Example of parasitism
Fleas feed on the host’s blood but don’t provide anything to the host in return
Examples of mutualism
• Bees gain nectar from flowers and they spread pollen as they visit different ones helping with reproduction
• Nitrogen fixing bacteria live inside root nodules of leguminous plants
• they fix nitrogen for plants
• bacteria gain nutrition and protection from plant
• Oxpeckers feed off parasitic insects that live on herbivores
• reduces disease in herbivores
Biodiversity meaning
The range and variety of different species in an area
Importance of biodiversity
High biodiversity ensures the stability of ecosystems and reduces the dependence on one species for:
• Food
• Shelter
• Maintenance of the physical environment
Methods of assessing abundance and distribution of organisms
• Quadrats
• Belt transects
Abundance meaning
The number of individuals of a species
Distribution meaning
How a species is spread through out an ecosystem
What is a quadrat?
A square frame used to collect samples and measure biodiversity
What is a belt transect?
A straight line that runs parallel with a suspected change in factor along which samples are taken
Formula for estimating the abundance of a species in an ecosystem
Total number of organisms in all quadrats x (total area sampled / area of quadrat)
How can we make samples more representative of an ecosystem?
• Increase the number of samples
• Use a random sampling method
Random sampling meaning
Collecting samples in an unbiased way
What are quadrats used to estimate?
The abundance of a species in an ecosystem (using random sampling)
How do we use a quadrat?
• The sampling area is converted to a grid format
• A random number generator is used to pick the sample points
• The quadrat is laid on the chosen sample point
• We can then estimate the abundance using the number of species in the quadrat
What are belt transects used to estimate?
The distribution of a species in an ecosystem (using systematic sampling)
How do we use a belt transect?
• Lay out a measuring tape in a straight line across sample area
• Place quadrats at regular intervals along the tape
• Measure the abiotic factors at each point to identify how it affects abundance
• Record abundance of each species within each quadrat
When plotting a graph, which variables goes on the x and y axis?
x-axis: Independent variable
y-axis: Dependent variable
What are the dependent, independent and control variables in the quadrats and transects practical?
Dependent variable: The abundance
Independent variable: Abiotic factor
Control variable: Quadrat (placed at top left corner)
Trophic levels meaning
The feeding relationships between organisms
Food chain meaning
Shows the transfer of energy from one organism to the next
What is energy stored as at each trophic level in a food chain/web?
Biomass
Maximum number of trophic levels in a food chain/web
Between 4 and 5
Why is the efficiency of energy transfer between trophic levels low?
• Energy is lost as it gets transferred
This is because:
• Organisms rarely eat every part of the organism they’re eating (eg bones which are inedible)
• Some ingested material is egested (excreted) as faeces
• Energy is absorbed for:
• Movement
• Heat generation
• Metabolic processes
What is a pyramid of biomass?
Shows how much mass the creatures at each level have without the water in them (dry mass)
Roughly what percentage of energy of each trophic level is passed on to the next?
10%
Characteristics and importance of nitrogen
• Needed to make proteins and DNA in plants and animals
• Is an unreactive gas
• Makes up about 78% of atmosphere
Describe the process of the nitrogen cycle (6)
• Both plants and animals need nitrogen in order to survive and grow, but neither can absorb the nitrogen in the air as it’s unreactive
• Animals get their nitrogen from digesting plants (or other animals), and plants must get their nitrogen from the soil (as nitrates or ammonium ions)
• Nitrogen fixing bacteria in the soil/root nodules of leguminous plants convert N2 gas into ammonium compounds
• Decomposers (fungi & bacteria) convert nitrogen compounds in waste and dead organisms into ammonia
• This forms ammonium ions in the soil
• Nitrifying bacteria converts ammonium ions into nitrites which are then converted into nitrates
• Denitrifying bacteria converts these nitrates into nitrogen gas during respiration and it gets released into the atmosphere
How does lightning contribute to the nitrogen cycle?
• It can split the bond between the 2 nitrogen atoms
• This turns them into nitrous oxides
• Forms a part of the nitrogen fixing process
Crop rotation meaning
• When different types of crops are grown in the same area in a cycle to improve soil health
• Usually includes nitrogen fixing crops
How is the haber process involved with the nitrogen cycle?
• It’s used to make fertilisers
• These provide the soil with nitrates which are absorbed by plants to support making protein and DNA
• This maximises plant growth
What are the 4 processes in the nitrogen cycle?
• Nitrogen fixation
• Ammonification
• Nitrification
• Denitrification
Characteristics and importance of carbon
• It’s always transferred as a molecule in the carbon cycle
• CO2 is required for photosynthesis
• Photosynthesis is the only process that takes carbon out of the atmosphere
Describe the carbon cycle (6)
• Carbon is absorbed from the atmosphere by plants during photosynthesis in the form of CO2
• The carbon is transferred to animals as they feed on it
• Carbon is released into the atmosphere in the form of CO2 as plants, animals and microorganisms respire
• When animals/(plants) excrete waste or die, decomposers feed on it transferring carbon in the process
• The carbon in dead plants and animals can also be converted into fossil fuels over millions of years under much pressure
• When fossil fuels are combusted, the carbon combines with O2 therefore CO2 is released into the atmosphere
Describe the water cycle
• Water enters the atmosphere as water vapour in two ways
• Energy from the sun heats the Earth’s surface and water evaporates from oceans, rivers, lakes
• Or when plant transpire releasing water vapour into the air
• The warm air rises taking water vapour with it
• The moist air cools down as it rises and water vapour condenses back into liquid water forming clouds
• Water returns to the earth in the form of precipitation
Why is water filtered?
To make it safe for human consumption, or potable, because it can contain substances harmful to health
Biomass definition
Mass of living organisms
Why do pyramids of biomass have a pyramid shape?
The mass of organisms decrease as you go up a food chain
In what form does energy enter a food chain/web?
As light (used by producers)
Formula for efficiency of biomass transfer
Biomass in higher trophic level
__________________________________ x 100
Biomass in lower trophic level
What factors affect the rate of decomposition?
• Temperature
• Water
• Availability of oxygen
Decomposition meaning
The breaking down and digestion of biological material (waste and dead organisms) by decomposers
Why is decomposition important?
It ensures that materials like carbon and mineral ions are recycled and returned to the environment
How does temperature affect rate of decomposition?
• At warmer temperatures, the enzymes involved have more kinetic energy to work at a faster rate which would increase the rate of reactions and decay
• However if it’s too high the enzymes would denature [meaning] and the rate of decay decreases
How does water affect rate of decay?
• As water availability decreases so does the rate of decomposition
• Decomposers require water to survive
• However if the soil becomes waterlogged, the rate of decay decreases as O2 availability falls
How does oxygen levels affect rate of decomposition?
Higher oxygen levels mean that decomposers respire more aerobically which gives them more energy to grow and decompose faster
What is compost?
A mixture of decayed organic material
What can compost be used as?
A natural fertiliser
How can we slow down the rate of decomposition?
• Low temperatures eg a fridge slows down the rate of enzyme activity and the reproduction of microorganisms
• Sealed food eg tinned food creates sterile conditions preventing microorganisms contaminating
• Using dried foods lack the water needed by microorganisms for survival therefore they won’t be able to grow on it
What 2 types of organisms carry out decomposition?
• Detritivores
• Decomposers
What are detritivores?
Organisms that break down organic matter into small pieces
What are decomposers?
Microorganisms that feed on dead organisms
Examples of detritivores
• Maggots
• Worms
• Beetles
Examples of decomposers
• Bacteria
• Fungi
Formula for rate of decomposition
change in mass
________________
time taken
Why is sea water not suitable for drinking?
It contains excess mineral ions (salts) which can lead to dehydration
Desalination meaning
Removing the excess mineral ions from the water to make it drinkable
What are 2 ways of achieving desalination?
• Distillation
• Reverse osmosis
What happens during distillation in desalination?
• Saline water is boiled
• The water vapour is funnelled through a tube
• The water vapour is condensed
• Pure water is collected
What happens during reverse osmosis in desalination?
• Saline water is forced at high pressure through a partially permeable membrane
• This filters out the mineral ions leaving pure water behind
What are indicator species?
Organisms whose presence indicates the presence or absence of certain types of pollution
What are the indicator species for water pollution?
• Bloodworms and sludgeworms (high levels of water pollution)
• Freshwater shrimps and stoneflies (clean water)
What are the indicator species for air pollution?
• Blackspot fungus on roses (clean air)
• Bushy lichen (clean air)
• Leafy lichen (mild pollution)
• Crusty lichen (more polluted environments)
• Absence of lichens (very heavy pollution)
What are lichens?
• Organisms that grow in exposed places such as rocks or tree bark
• Indicators of different levels of air pollution
What does water pollution consist of?
• Raw sewage or fertilisers (both having nitrates) are released into a body of water
• Microorganisms in the water increase in number
• Respiration increases and oxygen in the water is used up
What does air pollution consist of?
• Sulfur and nitrous dioxide being released into the atmosphere
• Fossil fuel is burnt
What is the advantage of using indicator species?
They’re cost effective
What are the disadvantages of using indicator species?
• Can’t give accurate quantitative figures for pollution levels
• Can be hard to see
• Specialists are required
What happens during eutrophication?
• Nitrates from nearby fertilisers enter a body of water due to surface runoff from precipitation
• Water pollution occurs and an algae bloom tends to occur (nitrate indicator)
• Light becomes blocked by algae
• Plants underwater die as they can’t photosynthesise
• Fish die as they lose prey and O2 levels decreased
How can the level of water and air pollution be assessed using living organisms?
[might come soon]
Why do farmers use plants like beans/peas for crop rotation?
• Increases nitrate levels in soil
• Because nitrogen fixing bacteria live on root nodules of peas/beans
• This converts nitrogen into nitrates
[Topic 7]
What chemical do endocrine glands release?
Hormones
How are hormones transported around the body?
Dissolved in blood plasma
What are the 6 main endocrine glands?
• Pituitary gland (master gland in brain producing FSH and LH)
• Thyroid (produces thyroxine)
• Pancreas (produces insulin and glucagon)
• Adrenal gland (produces adrenaline)
• Testes (produces testosterone)
• Ovaries (produces oestrogen and progesterone)
Function of glucagon
Controls blood glucose concentration
Target organ for glucagon
Liver/muscles
Effect of adrenalin on liver cells during excersise
• Glycogen is broken down into glucose
• Glucose is released by the liver
• Ensures a higher blood glucose concentration for increased respiration
How does the release of adrenaline result in improved performance of an athlete?
• The heart rate and blood pressure increases
• This increases blood flow
• Allows more glucose and oxygen to be delivered to muscle cells at faster rate
• Increases rate of aerobic respiration
• Therefore more energy can be released for movement
What does adrenaline do to blood vessels and why?
• It dilates (widens) vessels to allow more blood and glucose to be circulated
• Increases rate of aerobic respiration
What enzyme breaks down starch?
Amylase
What does the release of thyroxine stimulate?
The metabolism rate
What does LH mean?
Luteinising hormone
What does FSH mean?
Follicle stimulating hormone
What are the 2 hormones that keep thyroxine concentration stable?
• TRH (Thyrotropin releasing hormone)
• TSH (Thyroid stimulating hormone)
Describe process of negative feedback if thyroxine concentration is high
• High thyroxine levels inhibits the hypothalamus from releasing TRH
• This inhibits the pituitary gland from releasing TSH
• This inhibits the thyroid gland from releasing thyroxine
How does an underactive thyroid gland contribute to an increased body mass?
• Thyroid gland produces thyroxine
• Thyroxine regulates metabolic rate
• An underactive thyroid causes less thyroxine to be produced
• Metabolic rate therefore decreases
• So there’s a lower break down of carbohydrates and less energy being released
• Increases fat storage and body mass
How do hormones control the menstrual cycle?
• At the start, the pituitary gland releases FSH which causes the egg to develop in the follicle
• This stimulates the secretion of oestrogen in the ovaries and causes the uterus lining to thicken
• When oestrogen levels are high enough it stimulates the release of LH from pituitary gland causing ovulation
• Progesterone levels from corpus luteum start to increase in order to maintain uterus lining
• If egg is fertilised the oestrogen and progesterone levels remain high to maintain uterus lining
What happens if the egg is not fertilised by the end of the menstrual cycle?
• The corpus luteum breaks down
• The uterus lining breaks
• Progesterone levels drop
• This causes menstruation (period)
What day does ovulation occur?
Day 14
Control meaning
Point of comparison in an experiment
