IGCSE Edexcel biology revision cards of life processes.

Movement -  Animals move through the action  of muscles. Plants move through geotropism and hydrotropism.

Respiration- They respire to gain energy from nutrition.

Sensitivity -Living organisms are senitive to their surroundings.

Nutrition- Living organisms require nutrition to make food,as in plants,or eat other organisms.

Excretion - Living organisms get rid of toxic waste products.

Reproduction - Living organisms produce offspring.

Growth- Living organisms grow and develop by increasing in size and using materials from respiration.

MRS NERG

• A cell wall- A is a layer of non living material found on the outside of a cell. It is made of cellulose. It helps the cell keep its shape.
• A cell membrane- Forms a boundary between the cytoplasm of the cell and the ouside, it is not a complete barrier, some chemicals pass into and out of the cell, it is permeable to them. It controls which substances pass in either direction. We say that it is selectively permeable.
• A vacuole- A large central space surrounded by membrane . It is a permanent feature of the cell. It is filled with cell sap, a store of dissolved sugars, mineral ions and other solutes.
• A cytoplasm- Is the living material, it is a complex material made of many different structures, it helps substances move around the cell and is the site where most reactions take place.
• Mitochondria- Are found in cells that need a lot of energy, for example muscles and nerve cells. Mitochondria carry out most of the reactions of respiration.
• Chloroplasts- Are only found in plant cells, especially in the leaves, they absorb light in the process of respiration. Chloroplasts are green because they contain a green pigment called chlorophyll.
• A nucleus- Is the largest organelle, it controls the activities of the cell. It contains chromosomes, which carry the genetic material,or genes. Genes control the activities of the cell by determining which proteins the cell can make, one important group of proteins found in cells are enzymes.

• A cell membrane- Forms a boundary between the cytoplasm of the cell and the ouside, it is not a complete barrier, some chemicals pass into and out of the cell, it ispermeable to them. It controls which substances pass in either direction. We say that it is selectively permeable.
• A cytoplasm- Is the living material, it is a complex material made of many different structures, it helps substances move around the cell and is the site where most reactions take place.
• Mitochondria- Are found in cells that need a lot of energy, for example muscles and nerve cells. Mitochondria carry out most of the reactions of respiration.
• A nucleus- Is the largest organelle, it controls the activities of the cell. It containschromosomes, which carry the genetic material,or genes. Genes control the activities of the cell by determining which proteins the cell can make, one important group of proteins found in cells are enzymes.

Enzymes are proteins that increase the rate of reaction. They are biological catalysts, a catalyst is a chemical which speeds up a reaction without being used up itself. They are needed because temperatures inside organisms are low, without catalysts reactions that happen in the cell would be far too slow for life to go on.Cells contain hundreds of different enzymes,each catalysing a different reaction.

Genes---> Proteins (enzymes)----> Catalyse reactions

• The molecule that an enzyme acts on is called its substrate. 
• Each enzyme has a small area on its surface called the active site. 
• The active site is where the substrate attaches to the enzyme, and the reaction takes place and the products are formed.
• When the substrate joins up with the active site, it lowers the energy needed for the reaction to start,allowing products to be formed more easily 
• The substrate fits into the active site of the enxyme like a key fitting into a lock. That is why this is called the 'lock and key' model of enzyme action.

Extracellullar enzymes work outside cells, Intracellular enzymes work within cells.

The teperature at which an ezyme works best is called its optimum temperature, within the human body the optimum temperature is 37 degrees celcius. From 40 degrees celcius upwards the heat destroys the enzyme, we say it has been denatured, you can see the effect of this when you boil an egg.

The PH at which an enzyme works best is called its optimum PH, within the human body the optimum PH is 7,although some areas of the body have evolved to work at  a different PH. If the PH is too high or low the activity of the enzyme decreases, this is because the ph affects the structure of the enzyme, and changes the shape of its active site so that the substrate will not fit into it so well.

The chemical reactions taking place in a cell are known as metabolic reactions. The sum of all the metabolic reactions is known as the metabolism of the cell. So the function of enzymes is to catalyse metabolic reactions.

Respiration is the process by which an organism gains energy from nutrition. It gets this energy by breaking down food molecules to release the stored chemical energy that they contain. This is called cell respiration.

 This chemical energy can be used for a variety of purposes, such as:

• Contraction of muscle cells, producing movement.
• Active transport of molecules and ions.
• Building large molecules,such as proteins.
• Cell division

The energy released as heat is also used to maintain a steady body temperature in animals such as mammals and birds.

Glucose+ Oxygen ----> Carbon dioxide + water (+energy)                                                    C6H12O6 + 6O2    ------>        6CO2      + 6H20

This is aerobic respiration,because it uses oxygen, this process is carried out by all animals and plants and many other organisms. It happens gradually, as a sequence of small steps which release the energy of glucose in small amounts. Each step in the process is catalysed by a different enzyme. The later steps in the process are the aerobic ones, and these release the most energy. They happen in the cells mitochondria.

There are some situations where cells can respire without using oxygen. This is called anaerobic respiration. In anaerobic respiration, glucose is not completely broken down, and less energy is released. The advantage of anaerobic respiration is that little or no oxygen is required.

Two examples of anaerobic respiration.:

1. Yeast cells are used in commercial processes for making wine,beer and bread.  When yeast cells are prevented from getting enough oxygen, they stop respiring aerobically, and start to respire anaerobically instead. The glucose is partly broken down into ethanol (alcohol) and carbon dioxide.

Glucose ----> Ethanol + Carbon dioxide (+some energy)                                                      C6H12O6----   2C2H5OH  +   2CO2

2.  Muscles can also respire anaerobically when they are short of oxygen. If muscles are overworked blood cannot be pumped to them fast enough to to deliver enough oxygen for aerobic respiration. This happens when a person does a 'burst' of activity,such as a sprint. This time the glucose is broken down into a new substance called lactic acid. Although anaerobic respiration provides enough energy to keep the overworked muscles going for a short period of time, continuing the activity makes lactic acid build up, producing muscle cramp. The person then has to rest, to oxidise the lactic acid. This uses oxygen. The amount of oxygen needed to oxidise the lactic acid from anaerobic respiration is called the oxygen debt.

Glucose   ----> Lactic acid (+some energy)                                                                   C6H12O6 ----> 2C3H6O3

Many substances can pass through the membrane by diffusion. Diffusion happens when a substance is more concentrated in one place than another. The difference in concentration is called a concentration gradient. The molecules are constantly moving because of their kinetic energy, therefore the cell does not need any energy from respiration for diffusion to take place. The membrane is permeable to many substances, for example carbon dioxide, and allows it to move in either direction through the membrane.

If there were a higher concentration of carbon dioxide molecules inside the cell than outside, over time more molecules will move from inside the cell to outside. We say that there is a net movement of molecules from inside to outside.

The rate of diffusion of a substance is greater at higher temperatures. The reason for this is that a higher temperature will give the diffusing particles more kinetic energy.

So diffusion is the net movement of particles from a region of high concentration to a region of low concentration, i.e down a concentration gradient.

Active transport is the movement of particles against a concentration gradient, using energy from respiration.  An example of active transport is is in the human small intestine, where some glucose in the gut is absorbed into the cells lining the intestine by active transport, the roots of plants also take up certain mineral ions in this way.

So active transport is the the net movement of particles from and area of low concentration to an area of high concentration.

Water moves across membranes by a special sort of diffusion, called osmosis. Osmosis happens when the total concentrations of all dissolved substances inside and outside the cell are different. Water will move across the membrane from the more dilute solution to the more concentrated one ( this is still obeying the rules of diffusion)- the water moves from where there is a higher concentration of water molecules to a lower concentration of water molecules. Osmosis can only happen if the membrane is permeable to water but not to some other solutes. We say that it is partially permeable.

Osmosis is important for moving water from cell to cell, for example in plant roots.

So: Osmosis in cells is the net movement of water from a dilute solution to a more concentrated solution across a partially permeable membrane.

The rate of diffusion of a substance is increased by:

• A steep concentration gradient.
• High temperatures
• A large surface area to volume ratio ( red blood cells)

Diffusion is a slow process, organs that rely upon diffusion need a large surface over which it can take place . The alveoli (air sacs) allow exchange of oxygen and carbon dioxide to take place between the air and the blood,  during breathing.

Multicellular organisms begin life as a single fertilised egg cell, called a zygote. This divides into two cells, then four, then eight and so on, until the adult body contains countless millions of cells.

This type of cell division is called mitosis and is under the control of the genes. First of all the chromosomes in the nucleus are copied, then the nucleus splits into two, so that the genetic information is shared equally between the two 'daughter cells'. The cytoplasm then divides forming two smaller cells. These take in food substances to supply energy and building materials so that they can grow to full size. The process is repeated, but as the developing embryo grows, cells become specialised to carry out particular roles.

This specialisation is also under the control of the genes, and is called differentiation. Different kinds of cells develop depending on where they are located in the embryo, for example a nerve cell in the spinal cord.

• Cells with a similar function are grouped together as tissues. For example the muscle of your arm contains millions of similar muscle cells, all specialised for one function -contraction to move the arm bones. This is muscle tissue. However a muscle also contains other tissues, such as blood, nervous tissue and epithelium (lining tissue).
• A collection of several tissues carrying out a particular function is called an organ. Plants also have tissues and organs. Leaves, roots, stems and flowers are all plant organs.
• In animals, jobs are usually carried out by several different organs working togeter. This is called an organ system, for example the digestive system.

• Digestive system - including the gut , along with glands such as the pancreas and gall bladder. The function of the whole system is to digest food and absorb the digested products into the blood.
• Respiratory system - .including the lungs, which exchange oxygen and carbon dioxide
• Circulatory system - including the heart and blood vessels, which transport materials around the body.
• Excretory system- including the kidneys, which filter toxic waste materials from the blood.
• Nervous system - consisting of the brain, spinal cord and nerves, which coordinate the body's actions.
• Endocrine system- glands secreting hormones, which act as chemical messengers.
• Reproductive system - producing sperm in males and eggs in females, and allowing the development of the embryo.