Life Processes - 8 Life Processes
There are 8 Life Processes which are common to most living things:
Movement: by the action of muscles in animals, and slow growth movements in plants.
Reproduction: produce offspring.
Sensitivity: sensitive to changes in their surroundings.
Control: their internal conditions.
Growth: increase in size and mass, using materials from their food.
Respiration: get energy from their food.
Excretion: get rid of toxic waste products.
Nutrition: either they make their own food, as in plants, or eat other organisms, as animal do.
Life Processes - Animal and Plant Cells
Differences between animal and plant cells:
Animal cells Plant cells
Cell membrane Cell membrane
Life Processes - Definitions of parts of Animal an
Definitions of parts of animal and plant cells:
Nucleus: contains the genetic material.
Cell membrane: controls what goes in and out of cells.
Mitochondria: site of aerobic respiration, so they produce most of the energy needed by the cell.
Cytoplasm: where most of the chemical reactions take place.
Cell wall: strengthens and hold plant cells.
Vacuole: Full of cell sap, stores dissolved sugars, mineral ions and other solutes.
Chloroplasts: contain chlorophyll and are the site of photosynetheis.
Life Processes - Enzymes
Enzymes are biological catalysts, which speed up the reactions in the cell without being used themselves. Enzymes are needed because the temperatures inside an organism is low (e.g the human body temperature is 37`C) and this means without catalysts the reaction inside the cells would take too long.
The molecule that an enzyme reacts on is called its substrate and all enzymes have a small area on its surface called the active site. This substrate attaches to the active site of the enzyme where the reaction takes place and then products are formed (the substrate splits in half), which then leave the active site. This reaction is repeated over and over again as the enzyme is not affected by the reaction.
Life Processes - Factors affecting enzymes
There are 3 factors that affect enzymes:
1) TEMPERATURE: Enzymes in the human body have evolved to work best at about 37`C. This also known as the optimum temperature for the enzyme. When the temperature is increased the reaction is sped up, this is because higher temperaturesgive the molecules of enzyme and substrate more energy, so they collide more often. However when the enzymes in the human body go up 40`C or above the enzymes are destroyed or denatured. This is because the enzyme is made from protein and protein is broken down by heat.
2) CONCENTRATION: Either by increasing the concentation of the enzyme or the substrate.
3) pH: The pH inside cells is around neutral (pH 7) and this is known as the optimum pH. When the pH is more alkaline or more acidic the enzyme activity to decreases and this affects the structure of the enzyme molecule, and changes the shape of its active site so that the substrate will not fit into the enzyme anymore. However the pH in the stomach is 2 where the stomach makes the enzyme pepsin so this is the optimum pH for these enzymes and any lower or higher the pH the enzyme will be denatured.
Life Proceses - Aerobic and Anaerobic Respiration
The process of respiration happens in all the cells of our body. Oxygen is used to oxidised food, and Carbon Dioxide (and water) are released as waste products. The main food oxidised is glucose (a sugar). Glucose contains stored chemical energy that can be converted into other forms of energy that the cell can use. The energy released as heat is also used to maintain a steady body temperature in animals such as mammals and birds.
The overall reaction for aerobic respiration is:
Glucose + Oxygen = Carbon Dioxide + Water (+energy)
This is an aerobic respiration because it uses oxygen.
There are some situations where cells can respire without oxygen. This is called anaerobic respiration. In anaerobic respiration, glucose is not completely broken down, and less energy is released. One advantage of this process is that it can occur in situations where oxygen is in short supply. Two examples of this process are in yeast and muscle cells.
Life Processes - Aerobic and Anaerobic Respiration
Muscles cells can respire anaerobically when they are short of oxygen. If muscles are overworked, the blood cannot reach them fast enough to deliver enough oxygen. This can happen when a person does sprinting or lifts a heavy weight too quickly. In this process glucose is broken down into a substance called lactic acid. The equation for this process is:
Glucose = lactic acid (+some energy)
Anaerobic respiration provides enough energy to keep the overworked muscles going for a short period, but continuing the activity makes lactic acid build up in the bloodstream, producing muscle cramps. The person then has to rest, to oxidise the lactic acid fully. This uses oxgyen. The volume of oxygen needed to completely oxidised the lactic acid that builds up in the body durin anerobic respiration is called oxygen debt.
Life Processes - Diffusion, active transport and o
A cell membrane is selective about what chemicals can pass in and out of it, such as cells take in glucose and oxygen and get rid of carbon dioxide and water. There are 3 main ways molecules and ions can move through the membrane of a cell, diffusion, active transport and osmosis.
Many substances can pass through the cell membrane by diffusion. Diffusion happens when a substance is more concentrated in one place than another. This difference in concentration is called the concentration gradient. When the concentration gradient is greater on the outside of the cell, we say that there is a net movement from inside the cell to outside the cell. The rate of diffusion depends on the temperature. This means the higher the temperature the quicker the rate of diffusion is. This is because a higher temperature will give the diffusing particles more kinetic energy so they will move quicker across the membrane.
Active transport goes against the concentration gradient. This is done by using the energy from respiration to 'pump' ions and molecules out.
Life Processes - Diffusion, active transport and o
Water moves across cell membranes by a special sort of diffusion, called osmosis. Osmosis happens when the total concentrations of all the 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 or the water moves from where there is a higher concentration of water molecules to a lower concentration of water molecules just like diffusion. Osmosis can only happen across a partially permeable membrane. Osmos is important for moving water from cell to cell, for example in plant roots.
Life Processes - Cell division and differentiation
Multicellular organisms like animals and plants 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 genes. Firstly the 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 (or in plant cells a new cell wall develops) forming two smaller cells. These then take in food substances to supply energy and building materials so that they can grow to full size. This process is then repeated, but as the developing embryo grows, cells become specialised to carry out particular roles. This specialisation is also under 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 or an epidermal cell in the outer layer of the skin.
Life Processes - Cells, tissues and organs
Cells with a simiar function are grouped together as tissues and a collection of tissues is called an organ. Different organs working together are called the organ system. There are 7 of these systems:
Excretory system (e.g Kidneys)
Endocrine system (e.g Glands secreting hormones)