Biology Paper 1 Questions Selection

Compare the Functions of Organelles in Plant and Animal Cells

• Both have nuclei - to store DNA and control the cell
• Both have mitochondria - to produce energy through respiration
• Both have ribsomes - for protein synthesis
• Both have cell membrane - control what enters/exits the cell and to help prevent illness
• Both have cytoplasm - where chemical reactions take place

• Plant cells have a vacuole to store a sugary solution
• Plant cells have chloroplasts to 'capture' light - this is because plants must produce their own energy whereas animals eat food
• Plant cells have a cell wall to give it structure 

Describe the Process of Mitosis

1. DNA copies - chromosomes are duplicated

2. Metaphase - chromosomes line up in pairs down the middle

3. Anaphase - spindle fibres draw one from each pair of chromosomes away to opposite sides

4. Cell division - the cell splits down the middle

5. There are two identical daughter cells

This is an example of cloning or asexual reproduction because they offspring (daughter cells) are genetically identical

Describe How an Enzyme Works

• Enzymes are biological catalysts that speed up reactions in the body without being used up - they build up substances or break them down
• An enzyme has an active site that will only fit with a certain substrate (think lock and key model)
• The substrate fits into the active site and the enzyme will either break it down or make a new product
• The enzyme then releases the products and because it is a catalyst it is not used up so the process can happen again

Describe the Path that Blood Takes Through the Heart

• Blood enters throught the vena cava, and flows into the right atrium
• Passes through a valve into the right ventricle
• From here blood is pumped to the lungs to be oxygenated by the pulmonary arteries
• The pulmonary vein takes the oxygenated blood from teh lungs into the heart
• From the left atrium the blood passes through a valve into the left ventricle 
• Blood is then pumped out of the heart through the aorta to transfer oxygen to the reast of the body

A Burger is Eaten for Lunch. Describe how the Digestive System Breaks the Food Down

• Food enters the mouth where it is physically digested by the teeth which break it up, and the amylase enzyme chemically digests it by breaking starch into glucose
• The food passes down the oesophagus by peristalsis (muscle movement) and into the stomach where it is pummeled (physical)
• In the stomach, HCl acid kills microbes and the protease enzyme pepsin breaks protein into amino acids
• Bile is released into the small intestine to emulsify the fats and neutralise the HCl
• From the stomach the food passes into the small intestine where it is squeezed, and broken down by lipase, amylase and protease enzymes, and nutrients pass into the blood by diffusion
• After this, the food passes into the large intestine which extracts water
• What is left (roughage and waste) goes into the rectum and out the anus

How is the Small Intestine Adapted to Suit its Function?

• Conditions are correct for amylase, lipase and protease enzymes - food is broken downby these enzymes
• Thin walls of the small intestine increase the rate of diffusion
• Constant blood supply - maintains a steep concentration gradient to increase the rate of diffusion
• Villi - walls of the small intestine have villi which give it a large surface area to absorb as much food as possible quickly

How may Factors Limit the rate of Photosynthesis?

• Photosynthesis is the reaction in plants that converts carbon dioxide and water into glucose and oxygen
• Limitnig factors: carbon dioxide and water levels, temperature, light intensity
• The factors are needed in different quantities, and one or two will always limit the rate due to the lack of them
• Limiting reactants mean that there are not enough of one or both reactants for the reaction to take place 
• Lack of light - as light intensity increases so does the rate of photosynthesis because the reaction needs to convert energy (light energy from the sun) into energy (glucose). Therefore lack of light means there is not enough energy for the reaction
• Too low a temperature means the rate of reaction is slower, but too high a temperature will have the same effect

Explain how Oxygen Debt Occurs and how it can be Repaid

How it Occurs:

• Oxygen debt happens when the organism respires anaerobically (without oxygen, producing very little energy)
• Anaerobic respiration involves the incomplete breakdown of glucose, producing lactic acid
• Oxygen debt is the amount of oxygen required to oxidise the lactic acid into CO2 and water

Repaying Oxygen Debt:

• Build up of lactic acid leads to muscle fatigue, so the lactic acid must be oxidised to produce the products of aerobic (normal) respiration: carbon dioxide and water
• In order to do this, the body has to breathe deeply to take in a high volume of oxygen into the lungs
• Then the blood flow has to increase to transport the oxygen to the muscles quickly - this is why our hearts beats fast when we do intense exercise

Using Examples, Compare how Bateria, Fungi and Viruses make a Person ill

• Examples: bacteria = salmonella; virus = HIV; fungus = athletes foot

Comparison:

• All three are microscopic pathogens that enter the body
• Unlike the others, bacteria release toxins which cause the symptoms of illness
• Viruses act inside the body cells, and reproduce until the body cell bursts (lyse) - this causes illness as it is damage to cells
• Fungi feed off the body, so don't act inside the body in the same way as the other two 

How do Vaccines Work?

• Vaccines use a small amount of the pathogen that is either dead of inactive
• This is injected or consumed so that the white blood cells can then deal with the pathogen
• The white blood cells can find ways to deal with the unknown pathogen (e.g: producing special antibodies to fit the certain antigens of a bacteria)
• The memory white blood cells then remain in the bloodstream and will be able to recognise and deal with the pathogen if it's encountered again = the body reacts faster
• Because the body can react to or kill the pathogen faster, this means there are no symptoms because the pathogen doesn't have a chance to do anything