3.5 a 3.7 test Flashcards
What are the two key processes of the carbon cycle?
Photosynthesis and respiration
How does carbon enter the carbon cycle?
By photosynthesis. Carbon dioxide combines with water to make the sugar glucose.
How does carbon return back to the atmosphere during the carbon cycle?
By aerobic respiration and combustion of fossil fuels.
Why are plants often described as carbon neutral?
The carbon dioxide released by respiration is fixed by plants during the light independent stage (calvin cycle) of photosynthesis.
What is deforestation?
The complete removal of trees in order to use the land for another purpose, e.g. agriculture, building or infrastructure.
What are the three ways deforestation can increase CO2 content?
- A reduction in photosynthesis.
- An increase in combustion.
- An increase in decay.
How does a reduction in photosynthesis by deforestation increase CO2 content?
- The rate which CO2 is removed from the atmosphere is reduced.
- Less Carbon fixed into carbohydrates and other biological molecules by calvin cycle.
- CO2 remains in the atmosphere.
How does an increase in combustion by deforestation increase CO2 content?
- When trees are cut down, they may be burned to help clear the area for agriculture.
- Combustion releases CO2 into the atmosphere.
How does an increase in decay by deforestation increase CO2 content?
- Dead trees and vegetation left on the ground to decay.
- Decomposers (bacteria and fungi) multiply.
- These organisms release CO2 due to respiration.
Steps of carbon cycle:
- Co2 in atmosphere is fixed into carbs by light independent stage.
- respiration in plants and animals releases CO2 into the atmosphere due to action of decarboxylase in the link reaction and krebs cycle.
- Combustion of fossil duels releases CO2.
- decomposers release CO2 by respiration.
- carbon fixed into organic molecules by producers pass along food chains.
- Fossil fuels are formed over millions of years from dead remains
What is the nitrogen cycle?
The flow of organic and inorganic nitrogen within an ecosystem.
Why do living organisms need nitrogen?
to make amino acids, proteins and nucleic acids
Why are plants and animals unable to use nitrogen gas in the air?
because it is inert and unreactive.
What do plants and animals do since they can’t use nitrogen gas in the air?
Plants absorb nitrates in solution through their roots by active transport and the nitrogen contained within them is used to make amino acids, proteins and nucleic acids. These are then passed to animals through food chains.
What do nitrogen fixing bacteria/microbes do?
Convert atmospheric nitrogen directly into nitrogen compounds. These compounds are soluble and easily taken up by plant roots. (Microorganisms convert nitrogen gas to soluble compounds like ammonia)
What is the microbe Azotobacter
A free living aerobic bacteria found in the soil, which fixes nitrogen gas into soluble ammonia that can be absorbed by plant roots.
What is the microbe Rhizobium?
a symbiotic anaerobic bacteria found in root nodules of legumes such as peas, beans and clover. Converts nitrogen gas into soluble ammonia or ammonium ions using the enzyme nitrogenase - enzyme is inhibited by oxygen.
What surrounds the bacterium rhizobium?
Leghaemoglobin
What does leghaemoglobin do?
Prevents oxygen from reaching the anaerobic bacteria since it has a higher affinity for oxygen.
What is symbiotic relationships?
A relationship which both organisms derive benefit from
How is rhizobium and the legume plant in a symbiotic relationship?
The legume receives a soluble nitrogen source and the bacteria receives glucose and other products of photosynthesis.
What is Gross Primary Productivity?
The rate of production of chemical energy in organic molecules by photosynthesis in a given area, in a given time, so its units are kJ m-2 y-1
How to calculate net primary productivity?
NPP = GPP - respiration
What is net primary production?
That which is left over after respiration.
This represents the food available to primary consumers.
Both GPP and NPP are …… in plants which have a high photosynthetic efficiency.
Higher
What is the process of measuring biomass?
the process of determining the amount of organic matter in a sample of living organisms.
What is biomass?
a measure of the total organic matter in an ecosystem, including the living and dead plant and animal matter, as well as the organic material in the soil.
Strengths of pyramids of biomass
- Energy is incorporated into the macromolecules that make up biomass; so a pyramid of biomass is closely related to the energy passing through the system.
- Relationship between mass and energy so not misleading.
Weaknesses of pyramids of biomass
- Difficult to measure accurately e.g. roots are not always easy to harvest.
- May be inverted.
- Some trophic levels may seem to contribute more to the next trophic level than they actually do, e.g. bones have mass but don’t transfer energy.
What happens to pyramids of biomass in an aquatic system?
Can be inverted
Why is the mass of individuals present at a given time lower than the mass of zooplankton, which eat them?
Phytoplankton are the major producers.
A lot of energy flows through the first trophic level and the phytoplankton reproduce very quickly. Some are eaten immediately, leaving just enough to sustain the population.
What are consumers?
An animal that can’t produce their own complex materials, they must eat or consume them.
What are herbivores/ primary consumers?
Animals which feed on plants (producers)
What are carnivores?
Animals which feed on other animals.
What is ecological energetics?
The flow of energy through the ecosystem
What are producers?
Green plants, and producers absorb light energy and manufacture complex organic molecules from simple inorganic raw materials by photosynthesis.
What is a trophic level?
the organism’s position on a food chain.
What are detritivores?
Feed on dead remains and waste, and release energy trapped in the organic compounds in the tissues. Include wood lice, maggots and earth worms.
How does energy pass through trophic levels?
Energy passes from the producers at trophic level 1 to the herbivores at trophic level 2, and then on to the carnivores at trophic levels 3 to 5. Eventually, energy leaves the system as heat.
What is a food chain?
The sequence of energy transfers from plant to herbivore to carnivore which is the route by which energy passes between trophic levels.
Why is there a large loss of energy between trophic levels?
energy is lost through respiration and excretion of waste products.
What are the three main reasons light energy doesn’t stay in the leaf?
- reflected from the leaf surface
- transmitted through the leaf.
- wrong wavelength so not absorbed by photosynthetic pigments.
What is succession?
a sequence of changes, in the composition of a community, over time.
What will a succession eventually lead to?
a stable climax community with high biodiversity and is highly productive.
What is each stage of succession called?
A sere.
Where does primary succession begin?
From bare rock or the site of a recent volcanic eruption.
Who are the first organisms to colonise the rock?
The pioneer species, including lichens, mosses and algae.
How do pioneer species colonise the rock?
Change the rock surface by penetrating it and allowing humus to accumulate, which allows grasses and ferns to colonise the area
What do grasses and ferns do to rocks?
Further change the rock surface as their roots penetrate further and deeper.
What does death and decay over several generations do to rocks?
Allows more soil to accumulate and other higher plant species invade
What happens as the community of plants becomes more diverse?
Other organisms take advantage of the new habitats and food sources; the diversity of plants and animals increases and eventually a climax community is established.
How does a secondary succession begin?
Begins from bare soil
Why would a climax community from secondary succession be achieved faster?
Because the soil is already present and may contain viable bulbs, seeds and spores.
How can bare soil be exposed?
After a wildfire
How could human activity prevent a climax community from being achieved?
- grazing sheep.
- farming of land.
- deforestation and soil erosion
What is biodiversity?
The variety of living organisms that we find in a region
What is habitat biodiversity
The variety of different habitats we find in an area
What is species biodiversity
The variety of species living in a certain area
What is genetic biodiversity
The variety of genes and alleles in a species.
What is ultrafiltration?
Filtration of solutes under high pressure. From the blood plasma to the lumen.
Which parts are responsible for ultrafiltration
bowman’s capsule and the glomerulus.
What do small molecules do
Pass into the lumen of the bowman’s capsule as filtrate.
What is generated as the blood capillaries narrow
High hydrostatic pressure is generated in the capillary knot as the blood capillaries narrow.
How is blood entering the glomerulus separated from the space inside the Bowman’s capsule?
By two cell layers and a basement membrane.
How is a high hydrostatic pressure generated?
The afferent arteriole has a wider diameter than the efferent arteriole which provides the driving force for ultrafiltration.
How do the wall of the capillaries of the glomerulus allow ultrafiltration to take place?
The walls are only one cell layer thick (the endothelium) and there are tiny pores which allow solutes to pass to the basement membrane.
What are the tiny pores between endothelium cells called
Fenestrations.
How does the the basement membrane allow ultrafiltration to take place?
It’s a selective barrier which only allows small molecules through.
How do the squamous epithelial cells (podocytes) which line the bowman’s capsule allow ultrafiltration to take place?
Podocytes have finger-like projections called pedicels which wrap around the capillaries and pull them closer to th ebasement membrane.
Why does the blood that flows from the capillary knot of the glomerulus into the efferent arteriole have a low water potential.
Because much of the water has been lost as filtrate and there is a high concentration of proteins remaining in the blood plasma.
What is selective reabsorption
The process by which useful substances like glucose, amino acids and salts are reabsorbed back into the blood plasma as the filtrate flows along the nephron
Where and how does selective reabsorption happen?
In the proximal convoluted tubule (in the cortex) by facilitated diffusion and active transport.
How does the structure of the proximal convoluted tubule help selective reabsorption
- Cuboidal epithelial cells which line the walls are highly specialised.
- many mitochondria for ATP for active transport.
- tight junctions between the cells that encircle a cell and attach it to its neighbours which prevent molecules from diffusing between adjacent cells.
How does reabsorption of water by the loop of henle work?
Filtrate leaves the PCT and enters the descending limb of loop of henle which is permeable to water so water leaves the filtrate and enters the blood by osmosis, down a w.p gradient. At the same time, Na+ and Cl- ions diffuse into the descending limb from the medulla
How is the medulla’s low water potential maintained?
By the ascending limb of the loop of hele expelling Na+ and Cl- by facilitated diffusion then active transport.
What happens as water leaves the descending limb by osmosis
The filtrate becomes more concentrated, reaching maximum concentration by the apex of the loop
What does the ascending limb do?
Is impermeable to water but is permeable to Na+ and Cl- so they initially leave by facilitated diffusion but as concentration of solutes decrease, active transport takes over the expulsion of them into the tissue fluid of the medulla.
Steps of hair pin counter current multiplier
- Na+ and Cl- are pumped from the upper regions of the ascending limb by active transport.
- This decreases the water potential of the tissue fluid in the medulla of the kidney.
- Water is lost from the permeable descending limb of the loop of henle by osmosis from a high w.p in the descending limb to a low w.p in the tissue fluid of the medulla.
- The loss of water from the descending limb concentrates the filtrate.
- Na+ and Cl- ions diffuse out of the filtrate as it travels up the ascending limb. Later the ions will be pumped out by active transport as their concentration decreases in the loop.
- A highly concentrated region of salt forms deep in the medulla which lowers the w.p of the tissue fluid, so water leaves the permeable collecting ducts and is carried away by the vasa recta
What is osmoregulation?
The control of body fluid water potential by negative feedback - a type of homeostasis.
How does osmoregulation work?
-Osmoreceptors in the hypothalamus detect a decrease in the blood plasma water potential.
- A signal is sent to the posterior lobe of the pituitary gland which releases the hormone ADH into the bloodstream.
- ADH is carried to the kidneys and binds to receptor proteins on the wall of the collecting duct and distal convoluted tubule (the effectors).
- Aquaporins are added to the cell membranes of the effectors, allowing more water to be reabsorbed by osmosis. This increases the water potential of the blood back towards the set point
- This information is fed back to the hypothalamus and less ADH is produced
What does ADH do?
Increases the permeability of the collecting duct and distal convoluted tubule, allowing more water to be reabsorbed so urine produced will be more concentrated.
How are neurotransmitters released?
When an action potential reaches the presynaptic membrane, channels open to allow Ca2+ to enter the synaptic knob. Synaptic vessels containing neurotransmitter migrate towards the presynaptic membrane and fuse with it. The neurotransmitter is released by exocytosis. The neurotransmitter diffuses across the cleft and binds to receptors on post synaptic membrane which pens the Na+ channels and allow Na+ to flood into the post synaptic neuron. If sufficient Na+ enters the post synaptic neuron an action potential will be generated in that nerve cell.
What is haemodialysis
A type of dialysis which removes waste products and excess salts from the blood.
How does lysis occur?
Occurs in a hypotonic environment where water moves into the cell by osmosis and causes its volume to increase to a point the cell bursts.
How does haemodialysis work?
A pump pushes the blood through the dialysis tubing which is partially permeable to make sure large molecules like protein can’t leave. The tubing is suspended in dialysis fluid which contains pure water and no waste products. No waste products means as the blood flows through, a concentration gradient in created which allows waste products to be removed and into dialysis fluid by diffusion.
