Biology paper 1

• Benedict's solution is used to test for sugar. If sugar is present it will turn from blue to brick red but green/yellow/orange if less is present.
• Iodine solution is used to test starch. If starch is present it will turn from orange to black.
• Birruet solution is used to test protein. If protein is present it will turn from blue to purple.
• Ethanol solution is used to test for fats. If fat is present it will turn from colourless to cloudy.
• A stem cell is an undifferentiated cell. It has not yet specialised, so it has the ability to differentiate and form a specialised cell. A stem cell can divide by mitosis to form a tissue of stem cells.
• Coronary arteries that are blocked or have become narrow can be stretched open and a stent inserted to restore and maintain blood flow.

  Stents are used when drugs are less effective, and are a 'longer term' solution. Stents are made from metal alloys and do not lead to an immune response in the patient.

  Effects include : risk of bleeding, heart attack or stroke.
• Statins are drugs that help to lower cholesterol in the blood. They do this by lowering its production in the liver. They are prescribed to people with heart disease or who have a high risk of developing it. The drugs need to be taken long-term. 

  They should not be prescribed for people with liver disease, or pregnant or breast feeding women.

  Effects include : diarrhoea, headaches and feeling sick.
• A pathogen is a microorganism that causes a disease. There are four main types of pathogen:

  • Virus
  • Fungi
  • Protist
  • Bacteria

  All types of pathogen have a simple life cycle. They infect a host, reproduce themselves or replicate if it is a virus, spread from their host and infect other organisms.

  Diseases caused by pathogens are called communicable diseases. This means they can be transferred from one person to another.
• The xylem is a tissue which transports water and minerals from the roots up the plant stem and into the leaves. It doesn’t require energy.

  Xylem consists of dead cells. The cells that make up the xylem are adapted to their function:

  • They lose their end walls so the xylem forms a continuous, hollow tube.
  • They become strengthened by a substance called lignin. Lignin gives strength and support to the plant. We call lignified cells wood.
• The phloem moves food substances that the plant has produced by photosynthesis to where they are needed. Sucrose is the transport sugar in the phloem. This is called translocation. Translocation requires energy. Phloem consists of living cells.
• phloem adapted cells :

  • Sieve tubes - specialised for transport, have no nuclei. Each tube has a perforated end so its cytoplasm connects the cells. Sucrose and amino acids are translocated in the cytoplasm of the tubes.
  • Companion cells - transports substances in the phloem, requires energy. Companion cells attach to each sieve tube to provide energy. A sieve tube is dependent on its companion cells.
• During photosynthesis, plants produce glucose from simple inorganicmolecules (carbon dioxide and water) using light energy.

  Photosynthesis is an endothermic reaction. The light makes chemical reactions happen it is absorbed by chlorophyll. Chlorophyll is located in chloroplasts in plant cells, particularly the palisade and spongy mesophyll cells.

  The carbon dioxide for photosynthesis comes from the air and enters leaves through the stomata. Water enters the plant through the roots, and is transported to the leaves in the xylem.

  Oxygen is formed as the waste product.
• What is the photosynthesis equation ?

  Carbon dioxide + Water → Glucose + Oxygen + Water
• What is a prokaryotic cell ?

  Small, simple cells
• Bacteria doesn’t have chloroplast, mitochondria, or nucleus. Instead they have singular strand of DNA or plasmids.
• Animal cells : sub cellular structures + function :

  Nucleus - has genetic material that controls the cell

  Cytoplasm - chemical reactions happen here

  Cell membrane - holds the cell together and controls what goes in and out

  Mitochondria - reactions for aerobic respiration happen and transfers energy

  Ribosomes - where protein is made
• Plant cell : sub cellular structures + functions :

  Cell wall - made of cellulose and supports and strengthens the cell

  Permeant vacuole - contains sap (solution of sugar and salt)

  chloroplast - where photosynthesis happens and where chlorophyll is found

  Chlorophyll - absorbs light for photosynthesis

  Nucleus - has genetic material that controls the cell Cytoplasm - chemical reactions happen here

  Cell membrane - holds the cell together and controls what goes in and out

  Mitochondria - reactions for aerobic respiration happen and transfers energy

  Ribosomes - where protein is made
• Magnification = image size / real size
• Light microscopes use light and lenses to magnify objects. It allows us to see individual cells and large sub cellular structures such as nuclei.
• Electron microscopes use electrons to magnify objects. It lets us see smaller things in greater detail like the internal structure of a mitochondria or plasmids. It also has a higher resolution and gives us a sharper image compared to light microscopes.
• How to prepare a slide : microscopy :

  Add water to clean

  Cut an onion and spread out into layers

  Use tweezers to peel off some epidermal tissue

  Place the tissue onto the water

  Add iodine solution

  Place a cover strip

  try not to get any air bubbles
• The purpose of using iodine in microscopy is because it stains the cells blue/purple which makes them easier to see under the microscope
• How to use a microscope :

  Clip the slide onto the stage

  Select the lowest powered objective lens

  Look down the eye piece move the coarse objective lens to move the stage up until the image is in focus

  Adjust the focus with the fine adjustment knob until you get a clear image

  If you need a greater magnification use a higher powered objective lens
• Name six specialised cells.

  Nerve, sperm, muscle, root hair, phloem and xylem
• Chromosomes are coiled up lengths of DNA molecules. Humans have 23 pairs of chromosomes.
• Cell cycle :

  In a cell that’s not dividing the DNA is spread out in long strings

  Before it divides it has to duplicate sub cellular structures such as mitochondria

  Then mitosis takes place - the cell splits

  Cell Fibres pull them apart and go to opposite ends of the cell

  Membranes form around the chromosomes which is now the nuclei for the cells

  The cytoplasm and cell membrane divide

  These are now called daughter cells and they are identical to each other as well as the parent cell
• Multicellular organisms use mitosis to grow or replace cells that have been damaged.
• Give one reason against using stem cells from an embryo

  It takes away a potential human life
• Stem cells in plants are found in the meristems (where growth occurs). They can produce clones of whole plants quickly and cheaply which is important as it can save a rare plant as well as making plants disease resistant due to one plant being resistant all of its clones will be too.
• Diffusion = high concentration to low concentration
• Name one thing that can make diffusion happen quicker and why.

  Larger surface area, allows more particles to pass through
• Osmosis = high concentration to low concentration across a semi permeable membrane
• osmosis : practical :

  Cut up two potatoes

  weigh the potatoes

  Place both in separate beakers (the beakers should have different concentrated sugar solutions)

  Take out the potatoes and dry them with a towel

  weigh them again

  Increased mass = water has been taken in

  Decreased mass = water has being taken out
• Osmosis : practical :

  Dependant variable = potato mass

  Independent variable = concentration of sugar solution

  Errors could include :

  • Potatoes werent fully dried when weighted
  • Water was evaporated from the beaker

  To solve these you could :

  • Repeat Experiment
  • Work out a mean
• Active transport = low concentration to high concentration
• Active transport in humans :

  When there is a higher concentration of glucose and amino acids in the gut they naturally diffuse in the blood however sometimes their is a lower concentration so active transport has to take place allowing nutrients to still get into the blood.
• Gas exchange in humans :

  happens in the alveoli and small intestine

  alveoli (little air sacs) in the lungs allow the lungs to transfer oxygen to the blood and remove waste products such as carbon dioxide.

  The small intestine is covered in villi which increases surface area so that food can be absorbed much quicker into the blood.
• Name four adaptations of the alveoli.

  Large surface area, moist lining for dissolving gases, thin walls, good blood supply
• Name two adaptions of villi.

  Single layer of surface cells, very good blood supply for quick absorption
• Gas exchange in plants

  Happens in the leaf

  Carbon dioxide diffuses into the air spaces in the leaf and diffuse into the cells where photosynthesis happens. Stomata allows carbon dioxide, water and vapour to diffuse through, these are found on the underside of a leaf. water is lost through diffusion as there is more water in the plant than the air. The stomata is controlled by guard cells which will close the stomata if too much water is being lost.