Biology 4 (B4) - Specification



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

In sampling you have to:

  • take a big enough sample to make sure the results are 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 representitive of the population.

Also you must make previous assumptions when using the capture-recapture data:

  • no death, immigration or emmigration
  • identical sampling methods
  • marking not affecting survival rate.
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Ecosystem =  a physical environment with a particular set of conditions, plus all the organisms that live in it.

Habitat = part of the physical environment where an organism lives.

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.

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

A self-supporting ecosystem in all factors means that it provides mates, shelter but the one thing they rely on is an energy source (the Sun) and the producers that the bottom of the food chain.

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A transect line is used to map the distribution of organisms. 1. A line like a tap measure is laid out. 2.  Quadrats are distrubuted in regular interbals on the line, and the species in the quadrats are counted.

Kite diagram:


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Distribution 2

Zonation is a gradual change in the distribution of animals across a habitat.

A gradual change in the abiotic (non-living) factors (tides, water temperature, salinity of a rock pool) can result in zonation of organisms in a habitat. This is due to the different conditions created and an organism's optimum conditions.

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Biodiversity of natural ecosystems and artificial ecosystems:

  • natural ecosystems = high biodiversity - many different species of plant and animal coexist in the same environment.
  • artificial ecosystems = low biodiversity - designed and maintained for a particular purpose.

Forestry plantations are very carefully set up, controlled and monitored. They will have less biodiversity because they havent been established for as long as natural woodland. Fewer species are introduced at the setting up stage and not all species survive from the start.

Fish farms have less biodiversity due to the shorter time they have existed compared to lakes. Plus in the absence of predators, some species will thrive, others will not. Also, there are fewer diseases which may lead in too many of certain species reducing others.

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Development of the understanding of the process of photosynthesis:

  • the view of the greek scientists that plants gained mass only by tkaing in minerals from the soil
  • Van Helmont's experimental conclusion that plant growth cannot be solely due to the nutrients from the soil.
  • Priestly's experiment which showed that oxygen is produced by plants.

Using radioactive oxygen-18 (isotope), scientists dicovered 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 radioactive waste product of oxygen. This shows that photosynthesis is a two stage process. Firstly the light energy is used to split water, releasing oxygen gas and hydrogen ions. Secondly, the carbon dioxide gas combines with hydrogen ions to make glucose.

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Photosynthesis 2

Glucose and Starch can be converted into (IN PLANTS):

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

Insoluble substances such as starch are used for storage because:

  • does not more away in solution from storage areas
  • does not affect water concentration within cells.
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Photosynthesis 3

Photosynthesis can be increased by:

  • more carbon dioxide - limiting the rate of photosynthesis up to a point but from then after a rise in carbon dioxide doesn't effect the rate.
  • more light - limiting the rate of photosynthesis up to a point but after that a rise in light intensity doesn't effect the rate.
  • higher temperature - limiting factor in photosynthesis. As the temperature reaches 45 degrees, the enzymes controlling photosynthesis start to be denatured and the rate of photosynthesis declines to 0.

Plants carry out repiration all of the time because they need to break down glucose to release energy.

Plants take in carbon dioxide and give out oxygen during the day and do the reverse at night because during the day they are respiring during the day (but photosynethis happens faster) and only respiring at night.

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Parts of a Leaf


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Adaption of Leaves for Photosynthesis

Leaves are adapted for efficient photosynthesis:

  • broad so give a large surface area
  • thin so short distance for gases to diffuse
  • contain chlorophyll and other pigments to absorb light from different parts of the spectrum
  • have a network of vascular bundles for support and transport
  • guard cells which open and close the stomata.

The cellular structure also is efficient for photosynthesis:

  • epidermis is transparent - lets light through to layer below
  • palisade layer at the top containing most of the chloroplasts
  • air spaces in the spongy mesophyll allow diffusion between stomata and photosynthesising cells
  • internal surface area to volume ratio very large (efficient gaseous exchange)
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Photsynthetic Pigments

Leaves contain chlorophyll and other pigments which absorb different wavelengths of light.

  • 1. chlorophyll a +b
  • 2. xanthophylls
  • 3. carotene

All of pigments abosrb different ranges of colours of the light spectrum. The maximum rates are obtained in the red and violet ends. The greener colourred are reflected, this is why plants tend to be green.

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The net movement of particles by diffusion from an area of high concentration to an area of low concentration. Particles move about in lots of different directions. This is called random movement. Diffusion is the net (overall) movement of particles from a high concentration to a low concentration.

During the day in plants:

  • carbon dioxide used up in photosynthesis. The concentration inside the leaf is lower than outside.
  • carbon dioxide diffuses into plants through the stomata on the bottom of their leaves
  • oxygen, a product of photosynthesis, diffuses from the plant into the atmosphere.
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At night photosynthesis stops: oxygen diffuses into leaf cells and carbon dioxide diffuses out of leaf cells.

The stomata on the underside of leaves are specially adapted to:

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

The rate of diffusion is increased when:

  • there's a greater surface area of the cell membrane
  • there's a greater difference between concentrations (steeper concentration gradient)
  • the particles have a shorter distance to travel
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Osmosis is the net movement if water through a partially permeable membrane from an area of high water concentration to an area of low water concentration. As a consequence there is a random movement of individual particles.

Osmosis gradually dilutes the solution.

Osmosis is a type of diffusion.

Partially-permeable means a membrane that allows the passage of water molecules but not solute molecules.

You can predict the direction of water movement in osmosis by looking at the concentration of the water.

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Osmosis 2

Plants are supported by the turgor pessure within cells (water pressure acting against inelastic cell wall). The cell wall prevents cells from bursting due to excess water and contributes to rigidity.

Wilting is due to a lack of water. As the amount of water in the cell reduces, the cells become less rigid due to reduced turgor pressure.

Flaccid - not rigid due to lack of turgor pressure.

Plasmolysed - when the inside of the cell contracts due to cells losing alot of water.

Turgid - the inelastic cell walls withstand the pressure of the turgor pressure inside the cell increasing. The plant stands up right and is rigid.

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Osmosis 3

Uptake of water - increased osmosis so increased turgor pressure.

Loss of water - decreased turgor pressure/

Animal cells do not have inelastic cell walls.

Blood cells in a water solution gain water through osmosis. Without a cell wall to prevent water enetering the cell, they absorb more and more until they burst- LYSIS.

Blood cells in a concentrated solution will lose water through osmosis. Without a cell wall to prevent water loss, they can shrivel up and become crenated.

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Xylem and Phloem

Picture (

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Xylem and Phloem

Xylem - transpiration - movement of water and minerals from the roots to the leaves and shoots

Phloem - translocation - movement of food substances (sugars) up and down the stem to growing and storage tissues.

Both xylem and phloem form continuous systems in leaves, stems and roots.

  • Xylem vessels - thick strengthened cellulose cell wall with a hollow lumen (dead cells).
  • Phloem - columns of living cells.

Transpiration is the evaporation and diffusion of water from inside the leaves and it causes water to be move up the xylem vessels.

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Xylem and Phloem 3

Transpiration and water loss from leaves are a consequence of the way in which leaves are adapted for efficient photosynthsis:

  • the number, position, size and distribution of stomata very between plants, depending on their environment (which affects the amount of water they need)
  • the turgidity of guard cells changes in relation of the light intensity and availibility of the water, in order to alter the size of the stomatal openings.

Transpiration rate is increased by:

  • increase in light intensity - causes stomata to open - increases rate of evaporation
  • high temperature - increase movement of water molecules
  • increased air movement - blows water molecules away from the stomata
  • decrease in humitiy - increases the concentration gradient
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Root hairs have an enormous surface area for absorbing water so increase the plant's ability to take up water.

Transpiration provides plants with water for:

  • cooling
  • photosynthesis
  • support
  • movement of minerals

There are two more adaptations (as well as higher level answers) of how leaves reduce water loss:

  • a waxy cuticle
  • small number of stomata on the upper surface. Majority on lower surface.
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Plants need Minerals

  • Nitrates - for proteins which are needed for cell growth
  • Phosphates - for respiration and growth
  • Potassium - for respiration and photosynthesis
  • Magnesium - for photosynthesis

Elements obtained from the soil minerals are used in the production of compounds in plants:

  • nitrogen to make amino acids
  • phosphorus to make DNA and cell membranes
  • potassium to help enzymes in photosynthesis and respiration
  • magnesium to make chlorophyll.
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Plants need Minerals 2

Mineral deficiencies can result in poor plant growth:

  • nitrates - poor growth and yellow leaves
  • phosphate - poor root growth and discoloured leaves
  • potassium - poor flower and fruit growth and discoloured leaves
  • magnesium - yellow leaves

Minerals are usually present in soil in quite low concentrations.

Active transport:

Substances sometimes need to be absorbed from a low to a high concentration. It requires energy from respiration.

This is how minerals are taken up by root hair cells.

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Effects on the rate of decay:

  • temperature - microorganisms responsible for decay work best at around 40 degrees. Above this the enzymes become denatured and work slowly at low temperatures.
  • amount of oxygen - rate increases when oxygen increases. Increasing the amount of oxygen means that the microorganisms rate of respiration increases, producing more energy, enabling them to grow and reproduce quickly.
  • Amount of water - microorganisms grow quickest in moist conditions. Too much/too little will slow down their growth, and therefore, the rate of decay.

Detritivores, incliding earthworms, maggots and woodlice, feed on dead and decaying material (detritus).

Saprophyte - bacteria and fungi that feed on dead organic material.

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Decay 2

Detritivores increase the rate of decay by producing a larger surface area. This makes it easier for decomposers (bacteria and fungi) to feed on.

Saprophytic fungi digest dead material but secreting enzymes onto the material and then absorbing the digested products. This is extracellular digestion.

Food preservation methods reduce the rate of decay by removing the oxygen, moisture or warmth:

  • sealing inside sterile cans - prevents entry of decomposers
  • kept at low temperatures - slow down reproduction/growth of microorganims
  • pickled - acid kills
  • preserved in sugar or salt - removes water from the decomposers by osmosis, so killing them.
  • dried - reduces water
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Disadvantages of pesticides:

  • may enter food chains
  • may harm other organisms which aren't pests
  • some are persistant

Some plants can be grown without soil - roots in a solution containing all the minerals needed for growth. (HYDROPONICS)

  • greenhouses
  • plant growth with thin/barren soil

Advantages/Disadvantages of hydroponics:

  • better control of mineral levels and disease
  • lack of support for the plant
  • required addition of fertilisers
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Intensive Farming

Intensive farming may be efficient but they raise ethical dilemmas.Some people find this morally unacceptable because the animals have a poor quality of life.

Intensive food production improves the efficiency of energy transfer by reducing energy transfer:

  • to pests, including competing plants (weeds)
  • as heat from farm animals by keeping them penned indoors (battery farming) si that they are warm and move around less.
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Organic Farming

  • use of animal manure and compost
  • crop rotation including use of nitrogen fixing crops
  • weeding
  • varying seed planting times

Advantages of organic farming:

  • food crops and the enviornment aren't contaminated with artificial fertilisers or pesticides
  • soil erosion limited
  • biodiversity promoted
  • livestock have space to roam
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Organic Farming 2

Disadvantages of organic farming:

  • less efficient - some crops lost to pests and diseases
  • organic fertilisers take time to rot and they dont have a specific balance of minerals
  • it is expensive
  • more space needed
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Biological Control

Advantages: no need for chemical pesticides does not need repeated treament.

Disadvantages: predator may not eat the pest, may eat the useful species, may increase out of control, may not stay in the area where it is needed.

Important to remember that when biological controls or pesticides are used to get rid of pests, the effect on the rest of the organisms in the food chain or web must be considered. If the pest was the rabbits, this would also effect the organisms above it in the food chain who eat the rabbits.

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