Chemical reactions in living things : Processes of
M Movement All living things move - to find food, escape predators or find better growing conditions
R Respiration Getting energy from food to carry out cell processes
S Sensitivity Detecting changes in the surroundings such as light levels
G Growth All living things grow
R Reproduction Making new generations of a species
E Excretion Getting rid of waste - including carbon dioxide from respiration
N Nutrition Taking in and using food as a supply of energy
Chemical reactions in living things : Processes in
The cytoplasm of every cell in a plant contains a biological chemical factory. Different chemical reactions occur that serve different purposes. Some reactions help the plant to repair itself, some to copy itself and some to help it grow. Other reactions allow the plant to break down large food molecules to release energy in respiration.
Chemical reactions in living things : Enzymes
Enzymes are proteins that speed up chemical reactions in our cells.
Enzymes work best at their optimum temperature. This is why homeostasis is important - to keep our body temperature at a constant 37°C.
As the temperature increases, so does the rate of chemical reaction. This is because heat energy causes more collisions, with more energy, between the enzyme molecules and other molecules. However, if the temperature gets too high, the enzyme is denatured and stops working.
A common error in exams is to write that enzymes are killed at high temperatures. Since enzymes are not living things, they cannot be killed.
Chemical reactions in living things : Enzymes .2
Enzymes are specific. Only molecules with the correct shape can fit into the enzyme. Just like only one key can open a lock, only one type of enzyme can speed up a specific reaction. This is called the lock and key model.
Chemical reactions in living things : Enzymes .3
The important part of an enzyme is called the active site. This is where specific molecules bind to the enzyme and the reaction occurs.
Anything that changes the shape of the active site stops the enzyme from working. This is similar to a key that opens a door lock. It does not matter what a key handle looks like, but if you change the shape of the ‘teeth’ the key no longer works.
The shape of the active site is affected by pH. This is why enzymes will only work at a specific pH, as well as a specific temperature. Change the pH and the enzyme stops working.
Increasing the temperature to 60°C will cause a permanent change to the shape of the active site. This is why enzymes stop working when they are heated. We say they have become denatured.
How plants make food : Photosynthesis
Photosynthesis is a process used by plants in which energy from sunlight is used to convert carbon dioxide and water into molecules needed for growth. These molecules include sugars, enzymes and chlorophyll.
Light energy is absorbed by the green chemical chlorophyll. This energy allows the production of glucose by the reaction between carbon dioxide and water. Oxygen is also produced as a waste product.
This reaction can be summarised in the word equation:
Carbon dioxide + water glucose + oxygen
How plats make food : Photosynthesis .2
The chemical equation for photosynthesis is:
6CO2 + 6H2O C6H12O6 + 6O2
How plants make food : Glucose from photosynthesis
Glucose is made up of carbon, hydrogen and oxygen atoms. Glucose made by the process of photosynthesis may be used in three ways:
- It can be converted into chemicals required for growth of plant cells such as cellulose
- It can be converted into starch, a storage molecule, that can be converted back to glucose when the plant requires it
- It can be broken down during the process of respiration, releasing energy stored in the glucose molecules
How plants make food : Plant structure
How plants make food : Plant Structure .2
Chloroplasts - containing chlorophyll and enzymes needed for reactions in photosynthesis.
Nucleus - containing DNA carrying the genetic code for enzymes and other proteins used in photosynthesis
Cell membrane - allowing gas and water to pass in and out of the cell while controlling the passage of other molecules
Vacuole - containing cell sap to keep the cell turgid
Cell wall - strengthens the cell
Cytoplasm - enzymes and other proteins used in photosynthesis made here
How plants make food : Diffusion
Dissolved substances have to pass through the cell membrane to get into or out of a cell. Diffusion is one of the processes that allows this to happen.
Diffusion occurs when particles spread. They move from a region where they are in high concentration to a region where they are in low concentration. Diffusion happens when the particles are free to move. This is true in gases and for particles dissolved in solutions. Particles diffuse down a concentration gradient, from an area of high concentration to an area of low concentration. This is how the smell of cooking travels around the house from the kitchen, for example.
How plants make food : Diffusion .2
The movement of oxygen and carbon dioxide in and out of leaves during photosynthesis occurs by diffusion.
The higher concentration of carbon dioxide in the air diffuses into the leaf for photosynthesis.
Oxygen produced during photosynthesis builds up to higher concentrations and diffuses out of the leaf into the air which has a lower concentration of oxygen.
How plants make food : Osmosis
Water can move across cell membranes because of osmosis. For osmosis to happen you need:
- Two solutions with different concentrations
- A partially permeable membrane to separate them
Partially permeable membranes let some substances pass through them, but not others.
How plants make food : Osmosis .2
How plants make food : Osmosis .3
Osmosis is the movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane.
Eventually the level on the more concentrated side of the membrane rises, while the one on the less concentrated side falls. When the concentration is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. At this point, the net exchange of water is zero and there is no further change in the liquid levels.
Osmosis is important to plants. They gain water by osmosis through their roots. Water moves into plant cells by osmosis, making them turgid or stiff so they that able to hold the plant upright.
How plants make food - Minerals from the soil
The concentration of minerals in the soil is very low. They dissolve in water and move around the soil in solution. Root hair cells are adapted to absorb the water out of soil by osmosis – they have a large surface area, thin walls and are close to the xylem cells used for transporting water up the plant. Minerals such as nitrate ions cannot be absorbed by osmosis (which is the movement of water only) or diffusion (because the minerals are in very low concentration). The root hair cells have carrier molecules on their surface that pick up the minerals and move them into the cell against the concentration gradient. This requires energy, and is called active transport.
How Plants make food - Factors affecting photosyth
Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.
Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide
If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.
How plants make food : Maximising growth
Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses. They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a higher-than-normal light intensity. The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide, and heat too.
Obtaining energy : Energy from respiration
Glucose is produced during photosynthesis. This energy is released from cells by a series of chemical reactions. This process is called respiration. Energy from respiration is used in reactions that produce different molecules. Examples of these molecules include starch and cellulose, which are polymers of glucose required by plant cells.
Obtaining energy : Aerobic respiration
Respiration is not the same thing as breathing. Breathing is more properly called ventilation. Instead, respiration is a chemical process in which energy is released from food substances, such as glucose - a sugar.
Aerobic respiration needs oxygen to work. Most of the chemical reactions involved in the process happen in tiny objects inside the cell cytoplasm, called mitochondria.
This is the equation for aerobic respiration:
glucose + oxygen → carbon dioxide + water (+ energy)
C6H12O6 + 6O2 → 6CO2 + 6H2O
Obtaining energy : Aerobic respiration .2
The energy released by respiration is used to make large molecules from smaller ones. In plants, for example, sugars, nitrates and other nutrients are converted into amino acids. Amino acids can then join together to make proteins. The energy is also used:
- To allow muscles to contract in animals
- To maintain a constant body temperature in birds and mammals
Obtaining energy : Anaerobic respiration
Anaerobic respiration is a type of respiration that does not use oxygen. It is used when there is not enough oxygen for aerobic respiration. It can be summarised by the following equation:
glucose → lactic acid (+ energy released)
This type of respiration may be used when, for example, an animal is being chased by a predator.
Obtaining energy : Anaerobic respiration .2
Anaerobic respiration also takes place in plants and some microbial cells in the presence of little or no oxygen. Examples of this include the roots of plants in waterlogged soils and bacteria in puncture wounds.
Anaerobic respiration in plant cells and some microorganisms (such as yeast) produces ethanol and carbon dioxide, as opposed to lactic acid. It can be summarised by the following equation:
glucose → ethanol + carbon dioxide (+ energy released)
Aerobic respiration releases more energy per glucose molecule than anaerobic respiration.
Obtaining energy : Bacteria
Molecule of circular DNA Contains genetic code for enzymes involved in respiration Cell membrane Allows gases and water to pass in and out of the cell while controlling the passage of other chemicals Cell wall Provide rigidity to maintain cell shape Cytoplasm Enzymes are made and reactions involved in respiration occur here
Obtaining energy : Yeast
Nucleus Contains genetic code for enzymes involved in respiration Cell membrane Allows gases and water to pass in and out of the cell while controlling the passage of other chemicals Cell wall Provide rigidity to maintain cell shape Cytoplasm Enzymes are made and reactions involved in respiration occur here Mitochondria Contains enzymes for the reactions in aerobic respiration
Obtaining Energy : Useful products from respiratio
Anaerobic respiration of microorganisms such as yeast can lead to the production of useful commodities. During anaerobic respiration sugars are converted into ethanol. This is called fermentation.
When fermentation is performed on a larger scale using yeast, water, sugar and some other nutrients bioethanol can be made that can be used as a fuel.
Obtaining energy : Sustainability
Sustainability is the idea of using resources to meet the needs of the present without damaging the Earth or using up resources people might need in the future.
Biofuel is seen as a renewable resource that would seem to be more sustainable. However, there is more to it. The large areas of land used to grow crops on for biofuel could be used to grow food. As well as this, trees can be cut down to make space to grow crops for biofuel.
Obtaining energy : Biogas
Biogas is a fuel manufactured using animal manure (or sometimes human waste). Biodigesters are used to convert the manure into biogas. Bacteria inside the biodigester break down parts of the manure and produce methane gas. This gas can then be used as a fuel to run generators and heat buildings. This method of fuel production is more commonly used in developing countries.