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What is photosynthesis

Photosynthesis is a series of chemical reactions that use energy from sunlight to produce large food molecules


Name the large food molecules produced in photosynthesis



Glucose is a sugar


Where does photosynthesis occur

Photosynthesis occurs in green plants , particularly in the leaves

Photosynthesis also happens in phytoplankton which is a microorganism


What is needed for photosynthesis to occur

Light - serves as an energy source which fuels the reaction

Chlorophyll , is a green substance contained within the chloroplasts that absorbs the sunlight and applies this absorbed energy


The main stages of photosynthesis

1) light energy is absorbed by the green chemical chlorophyll

2) the energy absorbed is used to bring about a reaction between carbon dioxide and water to produce oxygen and glucose (large food molecules)

3) oxygen is released as a waste product


What are the reactants of photosynthesis

The reactants of photosynthesis are

- Carbon Dioxide

- Water


What are the products of photo synthesis

Glucose - large food molecules



Define photosynthesis

Photosynthesis is a series of chemical reactions that use energy from sunlight to build large food molecules in plant cells and some micro organisms for instance phytoplankton


What is the significance of photosynthesis to a food chain

Organisms that photosynthesis are found at the bottom of the food chain , they make energy available to other organisms by converting it to glucose . This energy can be transferred when the when the photosynthetic organisms are eaten therefore photosynthesis is important as it makes large food molecules (glucose )available to living organisms through the food chains. Photosynthesising organisms are producers .


What is the glucose produced in photosynthesis used for

1 - the glucose can be converted into chemicals needed for growth these chemicals could include cellulose for making new cell walls which would be especially useful if a plant was rapidly growing
The glucose could also be combined with nitrates to produce amino acids , amino acids are used to produce proteins and proteins are key to plant growth
The glucose could also be used to make chlorophyll which is the substance that absorbs the light energy to allow for photosynthesis , the plant can continue to survive providing it can power its photosynthesis hence the production of chlorophyll is very important

2) the glucose could be converted into starch where it could be stored in the roots stem and leaves , this reserved / stored energy can then be used in times when the rate of photosynthesis is lower for instance in the winter

3) glucose is a reactant in the chemical reaction of respiration , plants break down the large food molecules in the process and release carbon dioxide


Why may the rate of photosynthesis vary

The rate of photosynthesis may vary because of the environmental conditions a plant is exposed to for instance is it situated in an area of higher light intensity or a carbon rich atmosphere etc. There are 3 main factors that can have an impact on the photosynthetic rate

Carbon dioxide levels


Light intensity

If these factors are not accessible to the plant in a plentiful supply they become limiting factors and slow the rate of photosynthesis


Light / lights role as a limiting factor

If there is not enough light the rate of photosynthesis will be slower , lift provides the energy needed to commence the photosynthesis reaction . As light intensity increases this can only occur to a certain point until another factor begins affecting the rate of the reaction such as temperature or CO2 levels


Carbon dioxide as a limiting factor

Carbon dioxide is the raw material needed for photosynthesis if there is less available CO2 the rate of photosynthesis will be slower . Increasing the amount of CO2 available will only increase the tag of photosynthesis up until a point as after this something else will begin limiting the rate of the reaction such as temperature or light intensity


Temperature as a limiting factor

The enzymes needed for photosynthesis work more slowly in lower temperatures handed in higher temperatures the rate of photosynthesis is generally quicker. However if the temperature gets too hot the enzymes needed for photosynthesis will de nature and Janice the reaction will no longer be possible normally plant enzymes de nature at about 45 degrees


Adaptations impact on photosynthesis

If a plant has a adapted to low light conditions for instance if a large bush has grown in front of it then it will have evolved to have a lot of chloroplasts hence all light the plant can access is absorbed . If the bush is suddenly chopped down then the plant will be able to rapidly grow as it chloroplasts have a higher capacity for absorbing light energy as there is more of them , this rapid growth will not exponentially continue however as eventually another limiting factor such as the quantity of CO2 available or the temperature may begin to restrict the growth of the plant



Respiration is not breathing in or out it is a series of chemical reactions that break down large food molecules


Define respiration

Respiration is a series of chemical reactions that realise energy by breaking down large food molecules in all living cells


There are two types of respiration

Aerobic - with oxygen

Anaerobic -without oxygen


Aerobic respiration

Aerobic respiration needs oxygen , it realised more energy per glucose molecule than anaerobic respiration. We use aerobic respiration a majority of the time , it takes place in plant cells animal cells and some micro organisms


Reactants of aerobic respiration




Products of aerobic respiration

Carbon dioxide




Anaerobic respiration

Anaerobic respiration is the type of respiration that takes place in the instance there is no oxygen or a low supply of oxygen available , it can take place in animal cells or it can take place in plant cells as well as in some microorganisms


When could low oxygen conditions bring about anaerobic respiration

Human cells - when a human viceroyalty exercises the body cannot meet the demand for oxygen that they require hence anaerobic respiration begins in the muscle cells

Plant cells - if the soil a plant grows I becomes water logged there may be no available oxygen for the roots so the plant will begin anaerobic respiration. If this occurs they may not be able to take up nitrates as a lack of oxygen in the soil prompts anaerobic respiration which realises less energy per glucose molecule , as an implication the Plant may not have enough energy to undergo active transport which is needed for the uptake of nitrates as it moves them from an area of low concentration in the soil to an area of high concentration in the roots this moves them against the concentration gradient . Hence anaerobic respiration is a problem for a plant as amino acids are essential to growth as they are turned into amino acids which then form proteins/ enzyme which the plant needs to grow and function

Bacterial cells - if bacterial cells get under your skin via puncture wounds there will be very little oxygen as a consequence they will have to commence anaerobic respiration , only bacteria capable of anaerobic respiration can survive under the skin


What is the equation for anaerobic respiration in animal cells and bacterial cells

Glucose ----> lactic acid + ENERGY


What is the equation for anaerobic respiration in plant cells and some micro organisms like yeast

Glucose -----> ethanol + carbon dioxide + ENERGY



Fermentation is a process where micro organisms break down sugars like glucose into other products as they respire anaerobically . Humans use fermentation as useful products can be made thanks to the products of the reaction



Biogas is a fuel
Biogas is used for things like heating and lighting

To produce biogas humans ferment things like plant and animal waste which contain carbohydrates which are sugars . As the micro organisms break down the plant and animal waste (large food molecules ) in anaerobic respiration they produces gases such as Methane and carbon dioxide , these form biogas



Bread is made through the fermentation of yeast . The yeast ferment the carbohydrates in the flour and break some of these large food molecules down , in doing so they release carbon dioxide which causes bread to rise by producing bubbles of gas.



Yeast cells ferment sugar molecules in things like barley and grapes to produce ethanol (alcohol)


Why is respiration important ?

The basic processes of life carried out by all living things are dependent upon chemical reactions in cells that require energy released form respiration . This energy is used for

Movement - energy is needed for movement as it allows muscles to contract which brings about motion at the joints

Active transport - energy is needed to complete active transport to move substances in and out of cells against the concentration gradient

Synthesis of large molecules - lots of large molecules (polymers ) are made by joining smaller molecules together this requires lots of energy . Polymers need to be made but the body as it needs to connect molecules of glucose in chains to form substances such as cellulose for building cell walls in plants and starch to store sugars , plus nitrogen and glucose need to be connected to produce amino acids which are strung together to produce proteins .


So ...

Photosynthesis produces large food molecules through using energy stained from the sun

Respiration breaks down large food molecules to release energy needed for important processes in cells

Carbon dioxide is a product of respiration however it is also a reactant in photosynthesis , if respiration and photosynthesis are occurring at the same rate then the level of carbon dioxide will be constant


What are enzymes

Enzymes are proteins which speed up chemical reactions , without enzymes chemical reactions would occur very slowly


What are enzymes made of

Enzymes are proteins produced by living cells , cells make enzymes based on the instructions carried in the genes


Explain enzymes

Enzymes are very specific they are not one generic molecule. Chemical reactions normally involve things being split apart or joined together. The molecule that is going to be changed in the reaction is known as the substrate. Every enzyme has something which is known as an active site , the active site is the part where the substrate will lock into the enzyme . For an enzyme to work it's active sight must be complementary to the shape of a substrate , this is called a lock and key model as the substrate firsts the enzymes active site in the same way a key would fit a lock


What happens to an enzyme after a reaction

An enzyme is unchanged after a reaction it is not used up and hence can be used again and split or join more substrates of the reaction . An enzyme is a natural catalyst hence t speeds up the reaction without being used up


What is the optimum temperature of an enzyme

The optimum temperature of an enzyme is the temperature at which t is most active


What is the optimum pH of an enzyme

The optimum pH of an enzyme is the acidity or alkalinity that the enzyme is the most active within


What happens if optimum conditions change

If an enzyme gets too hot some of the bonds holding the enzyme together will break , this changes the shape of the enzymes active site , so the enzyme will no longer function anymore and is said to be 'denatured'. Of the pH gets to high the bonds holding the enzyme together will also be effected hence the shape of the active site will change which will meant he substrate cannot fit and the enzyme will be said to be de natured


Does the de maturing of an enzyme affect the collision rate

Even if an enzyme is denatured the collision rate will still increase with temperature only all collisions will be unsuccessful


Denatured enzymes

Once an enzyme is denatured it is permanent damaged therefore cannot be used again to speed up a reaction with a substrate . The process is irreversible


What temperatures do enzymes normally completely de nature by

Approximately 45 degrees


Every living thing is made of ...



What happens in cells

Chemical reactions occur in cells , this there are lots of organelles within different cells to allow the cells to carry out these reactions


Animal cells have a

The nucleus is the organelle which contains all the DNA , the DNA is that which contain the instructions for the production of proteins this the instructions for the production of enzymes

The cytoplasm is a hell like substance where proteins like enzymes are made , this is because the ribosome is located in the cytoplasm . Some enzyme controlled reactions also occur in the cytoplasm for instance anaerobic respiration

Cell membrane
The cell membrane of an animal cell holds the cell together and decides what can move in and what can move out acting as a filter . It lets water and gasses bass in and it while acting as a barrier to other chemicals

Enzymes needed go aerobic respiration are stored in the mitochondria, it is in this organelle that the reaction of aerobic respiration takes place


Plant cells have a

Cell wall
The cell wall is made from cellulose which is produced from glucose which is made in photosynthesis , it supports a plant cell and strengthens it

Cell membrane
A plant cell membrane holds the cell together and decide what goes in and out . It slows water and gasses to pass in and out while acting as a barrier to other chemicals

Enzymes needed for aerobic respiration are stored in the mitochondria it is in this organelles that the reaction of aerobic respiration takes place

The nucleus carries DNA / genetic code which is the instructions for protein synthesis hence allows the cell to produce proteins and enzymes used in chemical reactions such as photosynthesis

Chloroplasts contain chlorophyll and the enzymes needed for photosynthesis , they are green in colour as the chlorophyll has a green pigment and are the organelle where photosynthesis takes place

The cytoplasm is a gel like substance where proteins like enzymes are made , some enzyme controlled reactions occur in the cytoplasm for instance anaerobic respiration

The vacuole contains sap which is a weak solution of sugar and salts


Yeast cells contain

Cell wall
Cell membrane


A bacterial cell contains

Circular molecule of DNA not considered a nucleus
Cell membrane
Cell wall


How is a plant cell adapted to the reactions that it needs to carry out

So a plant cell carries out photosynthesis and respiration

The cell membrane allows oxygen to diffuse out as the product of photosynthesis and diffuse in as a reactant for respiration and allows the same to occur for carbon dioxide , in anaerobic respiration things like ethanol can also pass out through the cell membrane .

The cytoplasm is significant as it is the location from where protein synthesis takes place , proteins are the basis of enzymes and enzymes are the basis of chemical reactions which need to be completed for survival purposes such as to release energy and produce food

The nucleus is important as it contains the genetic code / instructions which informs organelles such as the ribosomes how to produce the proteins needed in the cell

Mitochondria are important as they contain enzymes for aerobic respiration , this is the reaction which provides the cell with most of its energy as it release more energy per glucose molecule than aerobic respiration



The levels of certain things in cells need to be controlled so that the cell can function properly . There are 3 main ways things move in and out of cells

Active transport



Diffusion is the passive overall movement of particles from a region of high concentration to a region of low concentration

When plants photosynthesis they take in carbon dioxide as the concentration of this is higher outside of the cell than it is inside the cell , they also loose oxygen by diffusion as the concentration of oxygen is greater inside the cell compared to outside so the oxygen moves out



Osmosis is a type of diffusion

Osmosis is the passive movement of WATER molecules from an area of low concentration to a region of high concentration over a partially permeable membrane. water molecules move from a dilute solution to a concentrated solution in order to try and balance the concentration of solution on either side of the membrane . He water molecules are those that move as they are the only molecules normally small enough to diffuse through the partially permeable membrane . A permeable membrane is a membrane that only allows certain substances to diffuse through .

Water is drawn up by the roots through osmosis , there is normally a higher concentration of solution in the plants roots than there is in the soil hence water is taken in to even the concentration gradient


Active transport

Active transport is the overall movement of chemicals across a cell membrane from a region of low concentration to a region of high concentration using energy released by respiration

Plants take in minerals and by active transport as the concentrations of nitrates and minerals in the root cells are normally greater than those in the soil , yet the plant needs to continue to take up nitrates and minerals for growth and development ( for instance to produce amino acids). Energy is needed for this process as it moves substances against their natural tendency / against the concentration gradient , this energy is produced by respiration.



Transects tell you how something changes over an area . To set up a transect you run a piece of string between two points , then start at one end of the transect and move across collecting all the data you want with each progression up / down the transect. You keep moving until you have collected data across the length of the transect . You can then analyse the data of the transect investigation to see how things like plant cover alter as thou move across different patches of land in a straight line this may be because some areas of the transect are shaded while others are not


To measure the effect of light on a plant you could

Use a light meter , you'd need to record the intensity of light in different areas of land should you be investigating the impact of light intensity on a plant , a light meter is a sensor that accurately measures how intense the light reaching an area is . It is a sensitive price of equipment


To improve the efficiency of data collection when doing field work you could

Use a quadrat. A quadrat is a square frame divided into 100 squares in a grid form . You can calculate the percentage of an area of land covered by a species of plant by counting how many squares are covered by the particular species if I treat you would count a square as full if over half of it is covered . When you are using a quadrat you must throw it to a random location to ensure the sample you take for a particular location is not bias


To identify different species in field work you may use a

Identification key , a identification key asked a series of questions and narrows down the number of possible species the plant in question could be with each response to a question about the aesthetic of the plant it does this until a single species remains and the plant is identified