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Flashcards in B4 Deck (131):

What is an ecosystem?

A physical environment with a particular set of conditions, plus all the organisms that live in it. An ecosystem can be natural or artificial.


Why is it that natural ecosystems have high biodiversity?

Because many different species of plants and animals coexist in the same environment.


Why do artificial ecosystems have low biodiversity?

Because they are grown and maintained for a particular purpose, and weedkillers, fertilisers and pesticides may be used to prevent other animals and plants from growing alongside the crop.


Why do forestry plantations have less biodiversity than natural woodland?

Because they haven't been established for as long as natural woodland, which takes years to form. Natural woodland results from the relationships and interactions of the organisms that live there, and their surroundings. In forestry plantations, fewer species are introduced at the setting up stage, and not all species survive from the start.


Why do fish farms show less biodiversity?

It's due to the short time that they have existed in comparison to lakes. Also, as there are many predators, some fish species will thrive while others will not, and fewer diseases may result in too many of certain species reducing others.


What is a habitat?

The part of the physical environment where an animal or plant lives. An organism will have adapted to its habitat, so it may be restricted to living there. It may only eat the food living there.


What is a community?

The total number of individuals of all the different populations of plants and animals that live together in a habitat at any one time.


What is a population?

The total number of individuals of the same species that live in a certain area.


Ecosystems are self-supporting in all factors, e.g. providing mates, shelter, but what do they all rely on?

An energy source [The Sun], and producers at the bottom of the food chain.


How can the the size and distribution of a population be measured?

With either pooters, sweepnets, pitfall traps or quadrats.


What are pooters?

Containers used to collect insects easily, without harming them.


What are sweepnets?

Nets used to collect insects in long grass or moderately dense woodland where there are lots of shrubs.


What are pitfall traps?

Containers set into the ground that are used to catch small insects such as beetles.


What are quadrats?

Square frames that have sides normally 0.5m long. They are used to count a small, representative part of a population. You should throw them on the ground randomly, and record the number of species within the quadrat. You can use that data to estimate the population of each species in a given area. Quadrat sizes can vary, dependant on the area you're surveying.


When sampling, what must someone make sure they do?

-Take a big enough sample to make the results a good estimate; the larger the sample, the more accurate the results.
-Sample randomly; the more random the sample, the more likely it is to be representative of the population.


What is 'capture-recapture', also known as the 'Lincoln Index'?

A method used to estimate a population size.


How does the 'capture-recapture' method work?

-A trap is used to catch a sample of individuals
-The sample is counted and recorded, and each individual is marked
-The individuals are released unharmed back into the environment, and are given time to redistribute themselves among the unmarked population
-another sample of individuals is captured. Some of them are already marked and some are unmarked.
-The unmarked animals are counted and recorded, then marked and released


What is the formula used with the capture-recapture method to estimate the total population size in the habitat?

population size = 1st sample x all in 2nd sample / number in 2nd sample previously marked


How does 'capture-recapture' work?

-a trap is used to catch a sample of individuals.
-the sample is counted and recorded and each individual is marked.
-the individuals are released unharmed back into the environment, and are given time to redistribute themselves among the unmarked population.
-another sample of individuals is captured. Some are marked, some are not.
-The unmarked animals are counted and then recorded, marked and released.


What is the formula that can be used to estimate the total population size in the habitat?

population size = No. in 1st sample [all marked] x No. in 2nd sample [marked and unmarked] / No. of prev. marked in 2nd sample


When using the capture-recapture method, what must be assumed?

No organisms have died, emigrated or immigrated between sampling.


What must be made sure of when using the capture-recapture method?

-Identical sampling methods are used from one visit to the next.
-Marking the organisms doesn't affect their survival [using too much paint on invertebrates could cause it to enter their respiratory passages and kill them]


What is photosynthesis?

The process by which green plants make their own food (glucose and starch) using sunlight


What did Joseph Priestley do?

Put a plant in a jar of air, and a plant in a jar with a mouse inside. He changed the combinations of plants and mice and concluded that oxygen is produced by plants.


What can the glucose produced in photosynthesis be converted into?

Energy (during respiration), proteins for growth and repair, starch, fats, or oils that can be stored in seeds, and cellulose, which is needed for plant cell walls.


How can can glucose be transported around the plant, and how must it be stored?

It can be transported around the plant as soluble sugar, but it must be converted into starch, which is insoluble, to be stored.


Why is starch a very useful storage molecule?

Because it's insoluble so that it doesn't affect the water concentration inside the cells where it's stored. It also does not move away in solution from storage areas.


What would happen if the cells stored soluble glucose?

The inside of the cells would become very concentrated and water would constantly move in through osmosis, which would make the cell swell.


Using radioactive oxygen-18, what did scientists discover?

That the oxygen produced as a by-product in photosynthesis comes from the water and not the carbon dioxide. Only when oxygen-18 is introduced via the water do you get a radioactive waste product of oxygen.


What does the fact that the oxygen produced as a by-product in photosynthesis comes from the water and not the carbon dioxide show?

That photosynthesis is a two-stage process. First, light energy is used to split water, releasing oxygen gas and hydrogen ions. Second, the carbon dioxide gas combines with the hydrogen ions to make glucose.


Why do plants grow faster in the summer?

Because they need light and warmth to grow


How can photosynthesis be increased?

By increasing:
-The temperature (using heaters in a greenhouse)
-The light intensity (using lamps in greenhouses)
-The carbon dioxide concentration (using chemicals, or as a by-product of using gas heaters in a greenhouse)


As the temperature rises, so does the rate of photosynthesis. What does this mean?

That temperature is the limiting factor in the rate of photosynthesis. As the temperature approaches around 45°, the enzymes controlling photosynthesis start to denature, and the rate of photosynthesis declines to 0.


As the carbon dioxide concentration rises, so does the rate of photosynthesis. What does this mean?

That carbon dioxide is limiting the rate of photosynthesis up to a certain point, after which a rise in carbon dioxide levels has no effect. So then, carbon dioxide is no longer the limiting factor; light intensity or temperature must be.


Why do plants give out oxygen during the day?

Because during the day, there is light available from the Sun so plants photosynthesise, taking in carbon dioxide to make glucose and releasing oxygen as a by-product.


Where does photosynthesis mainly occur?

In the leaves of plants


A leaf contains a pigment, chlorophyll in millions of chloroplasts, plus other pigments. How does this help with efficiency?

The pigment chlorophyll absorbs light, and the other pigments are to absorb light from different parts of the spectrum


A leaf is broad and flat. How does this help with efficiency?

As the leaf is broad and flat, it provides a huge surface area to absorb sunlight.


A leaf has a network of vascular bundles. How does this help with efficiency?

The network of vascular bundles provides support, and transports water to the cells and removes the products of photosynthesis, i.e. glucose.


A leaf has a thin structure. How does this help with efficiency?

The thin structure means that the gases (carbon dioxide and oxygen) only have a short distance to travel to and from the cells.


A leaf has stomata. How does this help with efficiency?

Stomata (tiny pores) on the underside of the leaf allows the exchange of gases; these are opened and closed by guard cells


In a typical leaf, the upper epidermis is transparent. How does this help with efficiency?

It allows sunlight through to the layer below


In a typical leaf, the cells in the palisade layer are near the top of the leaf and are packed with chloroplasts. How does this help with efficiency?

Because this means that they can absorb the maximum amount of light


In a typical leaf, the spongy mesophyll contains a lot of air spaces connected to the stomata. How does this help with efficiency?

Because this allows the maximum exchange of gases.


What happens in a plant during photosynthesis?

Carbon dioxide diffuses in through the stomata (leaf pores) and oxygen diffuses out through the stomata. Water is absorbed through the roots.


What are the four distinct layers of a leaf?

The upper epidermis, the palisade layer, the spongy mesophyll and the lower epidermis


Give an example of a plant cell which doesn't contain chloroplasts, and explain why.

Root cells do not contain chloroplasts because they obviously don't receive any light.


What is chlorophyll?

A mixture of pigments including chlorophyll a, chlorophyll b, xanthophylls and carotene.When lights of different colours are shone on chlorophyll a and b, they absorb different ranges of colours, but both tend to absorb colours in the red and violet ends of the spectrum.


How do substances move in and out of cell membranes?

By diffusion


What is diffusion?

The movement of a substance from a region of high concentration to a region of low concentration.


When is the rate of diffusion be affected?

-when there's a greater surface area of the cell membrane
-there's a greater difference between concentrations (a steeper concentration gradient)
-the particles have a shorter distance to travel


In terms of diffusion, what happens with plants during the day?

-Carbon dioxide is used up in photosynthesis. The concentration inside the leaves is lower than the concentration outside the leaves.
-Carbon dioxide diffuses into plants through the stomata (tiny pores) on the bottom of their leaves
-Oxygen, a product of photosynthesis, diffuses from the plant into the atmosphere


In terms of diffusion, what happens with plants during the night?

At night, photosynthesis stops. Oxygen diffuses into leaf cells and carbon dioxide diffuses out of leaf cells.


What are the stomata on the underside of leaves specially adapted to do?

open: to help increase the rate of diffusion of carbon dioxide and oxygen
close: to prevent excessive water loss in drought conditions.


What is osmosis?

The diffusion of water from high concentration of water (dilute solution) to low concentration of water (concentrated solution) through a partially-permeable membrane. Osmosis is a special type of diffusion involving water molecules. Plant cells are surrounded by a membrane which allows water to move in and out of the cells. Water and solute molecules move freely through the cellulose cell wall. The function of the cell wall is to provide support- it doesn't affect the movement of substances in or out of the cell.


What is a partially permeable membrane?

A membrane that allows the passage of water molecules but not solute molecules.


In osmosis, the water particles move randomly, colliding with each other and passing through the membrane in both directions. But, what is the net movement of molecules from?

The area of high water concentration to the area of low water concentration. This gradually diluets the solution.


How can you predict the direction of water movement in osmosis?

If you know what the concentration of the water is. Movement of water is always from high to low water concentration.


As well as plant cells, water also moves in and out of animal cells by osmosis. As animal cells don't have a cell wall, what problem could occur?

Too much water entering an animal cell could cause it to burst.


Using red blood cells as an example, describe osmosis in animal cells.

When red blood cells are in solutions with the same concentration as their cytoplasm, they retain their shape. When in a weaker solution, they absorb water, swell up and may burst. When in a more concentrated solution, they lose water and shrivel up.


Animal cells, unlike plant cells, don't have an inelastic cell wall. What does this mean for blood cells in pure water solution?

Blood cells in a pure water solution will gain water by osmosis. WIthout a cell wall to prevent water entering the cell, they absorb more and more water until eventually they burst. This is called lysis.


Animal cells, unlike plant cells, don't have an inelastic cell wall. What does this mean for blood cells in a concentrated solution (very little water)?

Blood cells in a concentrated solution will lose water by osmosis. Without a cell wall to prevent water loss, they can shrivel up and become crenated (have rough edges)


Plant cells have inelastic cell walls, which, together with the water inside the cells, are essential for the support of young non-woody plants. What does the cell wall do?

It prevents cells from bursting due to excess water, and contributes to rigidity.


What is the pressure of the water pushing against the cell wall called?

Turgor pressure


Describe how a lack of water can cause plants to droop (wilt).

As water moves into plant cells by osmosis, the pressure inside the cell increases. The inelastic cell walls can withstand the pressure and the cell becomes very turgid (rigid). When all the cells are fully turgid, the plant is firm and upright. But, if water is in short supply, cells will start to lose water by osmosis. They lose turgor pressure and become flaccid (not rigid) and the plant begins to wilt.


When cells lose a lot of water, the inside of the cell contracts. What is this called?



The xylem and phloem form a continuous system of tubes from roots to leaves, called vascular bundles. What do xylem do?

Xylem transports water and soluble mineral salts from the roots to the leaves (transpiration)


The xylem and phloem form a continuous system of tubes from roots to leaves, called vascular bundles. What do phloem do?

Phloem allows the movement of food substances (sugars) around the plant (translocation), up and down stems to growing tissues and storage tissues.


What are xylem?

Xylem vessels are made from dead plant cells. They have a hollow lumen, and the cellulose cell walls are thickened with a waterproof substance.


What are phloem?

Phloem cells are long columns of living cells.


Why do root hair cells increase the plant's ability to take up water?

Because they have an enormous surface area for absorbing water.


What is transpiration?

The diffusion and evaporation of water from inside a leaf. It causes water to be moved up xylem vessels and provides plants with water for cooling, photosynthesis and support, and brings minerals to the plant.


The transpiration stream is powered by the evaporation of water from the leaf. Describe this process.

-Water evaporates from the internal leaf cells through the stomata.
-Water passes by osmosis from the xylem vessels to leaf cells, which pull the thread of water in that vessel upwards by a very small amount.
-Water enters the xylem from root tissues, to replace water which has moved upwards.
-Water enters root hair cells by osmosis to replace water which has entered the xylem.


What can the rate of transpiration be affected by, and why?

High light intensity: this causes the stomata to open, which increases the rate of water evaporation.
High temperature: this increases the movement of the water molecules, which speeds up transpiration.
Increased air movement: this blows the water molecules away from stomata, which increases transpiration
High humidity: this decreases the concentration gradient, which slows down transpiration.


When the stomata is open, is the guard cell flaccid or turgid?



When the stomata is closed, is the guard cell flaccid or turgid?



A leafy shoot's rate of transpiration can be measured using a mass potometer. Describe this process.

-The plant's roots are submerged in a sealed bag of water and placed in a beaker.
-The beaker is placed on a digital balance
-Readings are then taken to see how much water is lost by the plant during transpiration
-The conditions, e.g. light, temperature etc, can be changed to see how this affects water loss.


Describe plants balancing the amount of water they take in and lose.

-Water is absorbed by the plant by the root hair cells, which have a large surface area to take in water.
-The water then diffuses through the plant up to the leaves
-When it reaches the leaves, it can be lost by transpiration.


Which adaptations reduce the rate at which water is lost from leaves?

A waxy cuticle on the surface of the leaf, and having the majority of the stomata on the lower surface of the leaf. Also, the number, position and size of stomata vary between plants, depending on their environment, which affects the amount of water they need, and the turgidity of guard cells changes in relation to the light intensity and availability of water, in order to alter the size of the stomatal openings.


What do the guard cells in a plant do?

During photosynthesis, the guard cells become turgid and the stomata are fully open. However, if there's a lack of water, the guard cells become flaccid and the stomata close to prevent unnecessary water loss and photosynthesis.


Why are transpiration and water loss an unavailable consequence of photosynthesis?

Because, although stomata are needed for the exchange of gases during photosynthesis, they also allow water molecules to pass out of the leaf.


Why are essential minerals needed, and how are they absorbed by plants?

They're needed to keep plants healthy and growing properly, and plants absorb dissolved minerals in the soil through their roots.


Why do farmers use fertilisers?

Because, although essential minerals are naturally present in the soil, they're usually in quite low concentrations. So, farmers use fertilisers containing essential minerals to ensure that the plants get all the minerals they need to grow.


What are the four essential minerals?

Nitrates (N), potassium compounds (K), phosphates (P) and magnesium (Mg).


What are nitrates used for as essential minerals?

To make amino acids that form proteins for cell growth


What are potassium compounds used for as essential minerals?

To help the enzymes in respiration and photosynthesis


What are phosphates used for as essential minerals?

To make DNA and cell membranes, and for respiration


What is magnesium used for as an essential mineral?

To make the chlorophyll for photosynthesis


What does a lack of nitrates in the soil cause?

Poor growth and yellow leaves


What does a lack of potassium in the soil cause?

Poor flower and fruit growth, and discoloured leaves.


What does a lack of phosphates in the soil cause?

Poor root growth, and discoloured leaves


What does a lack of magnesium in the soil cause?

Yellow leaves


How are experiments carried out t see how removing one essential mineral affects the plant?

The plant is grown in a soilless culture, in which the minerals can then be carefully controlled and changed.


What is active transport?

Sometimes, substances need to be absorbed from a low to a high concentration area, i.e. against a concentration gradient. This is called active transport, and it requires energy from respiration. Plants absorb mineral ions through their root hairs by active transport.


What is decay?

Decay is a process involving the breakdown of complex substances into simpler ones by microorganisms. The key factors in the process are microbes, temperature, oxygen and moisture.


The rate of decay is affected by several factors. How does temperature affect it?

Microorganisms work slowly at low temperatures, but at high temperatures (above 40°C) their enzymes are denatured and decay stops. They work best around 40°C.


The rate of decay is affected by several factors. How does amount of oxygen affect it?

Increasing the amount of oxygen increases the microorganism's rate of respiration, which leads to them producing more energy, enabling them to grow and reproduce more quickly. The more oxygen there is, the faster they grow.


The rate of decay is affected by several factors. How does amount of water affect it?

Microorganisms grow quickest in moist conditions. Too much or too little water will slow down their growth, and, therefore, the rate of decay.


What are earthworms, woodlice and maggots known as, and what do they do?

They're known as detritivores, and feed on dead organisms and decaying material (detritus) produced by living organisms.


How do detritivores speed up the process of decay?

By breaking down detritus (decaying material) into small particles which have a large surface area. This makes it easier for decomposers (bacteria and fungi) to feed on.


What are microorganisms used to break down?

human waste in sewage treatment works, and plant waste in compost heaps.


Why can materials that decay be recycled?

Because decaying materials release minerals back into the soil. Plants use these minerals to grow.


What are saprophytes?

Fungi are saprophytes; they feed on dead organic material by secreting enzymes onto the material and then absorbing the digested products. Saprophytes are essential for decay.


How can food be preserved?

By removing the oxygen, warmth, or moisture that the microorganisms need to grow or survive.


Why does being sealed inside sterile cans help preserve food?

Because it prevents the entry of decomposers


Why does being kept at low temperatures in a fridge or freezer help preserve food?

Because this slows down reproduction of the microorganisms growth


Why does being pickled in vinegar help preserve food?

Because acid kills the decomposers


Why does being preserved in sugar or salt help preserve food?

This removes the water from the decomposers by osmosis, killing them


Why does being dried help preserve food?

This reduces the water


Describe an experiment to show decay caused by microorganisms

1- Pour a solution containing nutrients into a flask (Flask A)
2-Melt and shape the neck of the flask.
3-Boil the nutrient solution to kill the microorganisms and drive out air.
4- Seal the neck of the flask
5-Pour some more of the same nutrient solution into another flask (Flask B). Repeat steps 2-3, but this time snap the neck of the flask off.

The solution in the flask with the snapped neck (Flask B) will start to decay within days because microorganisms will be able to enter the flask. But, the solution in the other (Flask A) will show no signs of decay as long as it remains sealed.


What do intensive farming methods aim to do?

Produce as much food as possible from the available land, plants, and animals.


Why does intensive farming use chemicals like pesticides?

To kill pests that damage crops or livestock, so more food is produced.


What are pesticides used to do?

Kill pests, i.e. any organism that can damage crops or farm animals.


What are insecticides used to do?

Kill insect pests


What are fungicides used to do?

Kill fungi


What are herbicides used to do?

Kill weeds which compete with crops for water and nutrients.


Why does care need to be taken when dealing with pesticides?

Because they can harm other organisms (non-pests), they can build up (accumulate) in food chains, harming animals at the tops, and some pesticides are persistent; they stay in the food chain for years


How does intensive farming increase productivity?

Keeping animals warm and penned up inside (battery farming) so that they cannot move improves the energy transfer by reducing the amount of energy lost at each stage of the food chain.


What are some examples of intensive farming?

Battery farming, glasshouses, hydroponics and fish farming


What is the con to intensive farming?

It can raise ethical dilemmas; some believe that it's morally unacceptable because the animals have a poor quality of life. For example, battery farming is very cruel to the hens as they are kept in such small, confined spaces, and suffer health problems due to this.


What do organic farming methods aim to do?

Produce food without the use of chemicals, so minimising the impact on the environment (no pesticides, no fertilisers).


What do organic farming methods include?

-Using natural fertilisers like animal manure or compost.
-growing nitrogen-fixing crops like peas or clover
-rotating crops to maintain soil fertility
-avoiding chemical pesticides by weeding
-varying seed-planting times to discourage pests


What are the advantages of organic farming?

-Food crops and the environments aren't contaminated with artificial fertilisers or pesticides.
-Soil erosion is limited, and fertility is maintained through the use of organic fertilisers
-Biodiversity is promoted because hedgerows and other habitats are consered
-Livestock have space to roam


What are the disadvantages of organic farming?

-It's less efficient because some crops are lost to pests and diseases
-Organic fertilisers take time to rot and don't supply a specific balance of minerals
-It is expensive
-More space is needed


What is 'hydroponics'?

A way of growing plants without using soil. The plants are grown with their roots in a solution containing the minerals needed for growth. This growing method is useful for greenhouses or areas which may have thin or barren soil. Certain plants, such as tomatoes, can be grown hydroponically in greenhouses.


What are the advantages of hydroponics?

-The mineral levels added to the solution can be carefully controlled and adjusted to the type of plant
-There is a reduced risk of the plants becoming diseased.


What are the disadvantages of hydroponics?

-The plants have to be supported as there is no anchorage for their roots
-Expensive fertilisers are needed to supply the plant with minerals.


What is biological control?

When farmers choose to introduce a predator in lieu of a pesticide, to reduce the number of pests.


What is it important to remember when using biological control or pesticides?

When biological controls or pesticides are used to get rid of pests, the effect on the rest of the organisms in the food web must be considered. For example, if a pest control was used to target rabbits, the effect would be not just on the rabbits, but also on the predators that eat the rabbits, e.g. foxes, hawks.


What are the advantages of biological control?

-The predator selected only usually attacks the pest, as it's species-specific
-Once introduced, the predator can have an effect over many years, so repeating treatment isn't required
-The pest can't become resistant to the predator, unlike pesticides
-There's no need to use chemical pesticides


What are the disadvantages of biological control?

-The pest is reduced but not completely removed
-The predator may not even eat the pest, or may even eat useful species.
-The predator may reproduce out of control
-The predator may leave the area.