Exam Questions Flashcards
how do assimilates move from sieve tubes in leaves to sinks
mass flow
Sucrose decreases water potential
water enters sieve tubes down water potential gradient by osmosis
This causes an increase in hydrostatic pressure
Unloading of sucrose at the sink causes a decrease in hydrostatic pressure
Movements from source to sink is a gradient in hydrostatic pressure.
Advantage of plasmodesmata between cells in leaves
Increased diffusion of assimilates
Because more symplastic pathways.
How is the structure of the xylem vessel suited to its function
Transport of water and mineral ions
Elongated tubes for transport
No end wall so minimal resistance to flow of water
No organelle so more space for greater volume of flow
Cellulose walls allows adhesion of water molecules
Lignified walls prevent inward collapse and are waterproof so prevent loss of water
Pits allow lateral movement of water
Narrow diameter of lumen allows for adhesion
How is phloem transported from a stem to a fruit
Sucrose is loaded at source
Companion cells pump out H+ ions and sucrose moves in through co-transporter cells.
Water enters via osmosis
Hydrostatic pressure builds
Mass flow
Sucrose unloaded at sink gives a difference in hydrostatic pressure
Describe the process of gas exchange in healthy lungs and how is this impaired with someone who has emphysema (4)
In healthy lungs
1-Oxygen enters the blood from the alveolus and CO2 goes from blood to alveolus.
2- This is done by diffusion
3-Across the alveolar and capillary walls.
4- There is a higher rate of exchange with the healthy lung then the diseased lung
5- The healthy lung has a larger surface area for gas exchange
What type of plant is adapted to live in regions with low water supply (1)
Xerophytes
What part of the vascular tissue contains sucrose (1)
Phloem
Suggest why glucose is present in phloem sap (2)
1- Movement in sucrose from source to sink
2- The source is where the sucrose is synthesised, the sink is where it is stored
What is meant by hydrolysis of ATP (2)
Using water to break bond between phosphate group
What type of transport move K and Na ions (1)
Active transport
How do non competitive inhibitors affect the enzyme (4)
1- They reversible bind to a site other than the active site
2- Which changes the tertiary structure of the active site
3- The substrate can no longer fit into the active site
4- So less reactions can take place
Describe the sequence of events which occur in the left side of the heart during one normal cardiac cycle (4)
The left atrium fills with blood during relaxation of the left atrium and ventricle. Atrioventricular valve opens, the atria contracts increasing pressure and blood flows to the ventricle. The ventricles contract increasing the pressure in the ventricles. The bicuspid valve closes and semi-lunar valve opens. Blood flows into aorta
Suggest how the health of someone with heart failure could improve with drugs (3)
1- More powerful contractions of cardiac muscle.
2- Blood pumped at higher pressure.
3- More force required to overcome resistance in blood vessels.
4- More blood reaches lungs to obtain oxygen.
5- Less fatigue
Explain the importance of mitosis in the repair of damages tissue (2)
Devision produces new genetically identical daughter cells which retain function
Why are stem cells important in tissue repair (2)
Stem cells continuously divide. To produce cells that can differentiate. Can produce cells that can still function.
How are cells released in circulation to stimulate liver cells an example of cell signalling (3)
1- the chemicals released are cell signalling molecules
2- Liver cells are target cells
3- Binding of chemicals to receptors
4- The chemicals are complementary to receptors
Outline the key structures of viruses (3)
Protein coat made from capsomeres
Nucleic acid
DNA or RNA
Acellular
What is the global importance of HIV positive (but who do not have AIDs) pregnant and breast feeding women being on medication?
1- Because HIV can be passed from mother to child.
2- Reduces the number of HIV positive women becoming ill.
3- Reduced spread of HIV, the child may grow up without HIV and will not pass it on
4/5- Healthy women can contribute to workforce. Can be main carer if partner has died. Makes breastfeeding safer when there are no other options.
Explain why RNA can be described as a polymer and macromolecule (2)
Many monomers repeating, it is a large biological molecule
Outline the test and result for reducing sugars (2)
Add Benedict solution and boil. Precipitate changes to red
State the function of the Golgi body
Processing of proteins
State the function of centrioles (1)
Formation of spindle fibres
State the part of the haem group that binds to oxygen in each haemoglobin polypeptide (1)
Iron
State the compound formed when CO2 binds to haemoglobin (1)
Carbaminohaemoglobin
State the compound formed when hydrogen ions bind to haemoglobin (1)
Haemoglobinic acid
Function of vacuole (1)
Maintains turgor
Two structures in a cell which contain DNA
Nucleus, chloroplast
Why can you see the internal structures of cell organelle only with an electron microscope (3)
This is because a light microscope has a lower resolution then the electron microscope, with a resolution of 200nm and 0.5nm respectively. Resolution is the ability to see 2 point as different instead of just one point.
Describe the permeability of the cell wall and cell surface membrane (4)
The cell surface membrane is composed of a phospholipid bilayer. It has a hydrophobic interior meaning that polar and water soluble ions cannot pass through but lipid soluble molecules can. The cell wall has pores meaning that it is freely permeable to all molecules. The cell surface membrane has carrier and channel proteins meaning that water soluble molecules can pass through.
Osmosis
Large ion concentration lowers water potential, water moves from a high to low water potential down a water potential gradient.
Function of cell surface membrane
Controls the movement of substances in and out of the cell
Function of nucleolus
Production of ribosomes
Function of mitochondria
Aerobic respiration, synthesises ATP
Function of smooth endoplasmic reticulum
Synthesises lipids
Function of rough endoplasmic reticulum
Protein synthesis
Function of lysosomes
Contains digestive enzymes
Why is the cell surface membrane called a fluid mosaic model
Fluid= Molecules move about the membrane, ie phospholipid and protein molecules move about.
Mosaic = The protein molecules are scattered along the membrane, there are many different protein molecules
Explain why sodium ions cross the cell surface membrane by facilitated diffusion
Sodium ions are hydrophilic, they cannot pass through the hydrophobic interior. So they must pass through the hydrophilic transport proteins. Active transport is the only way to move sodium ions against the concentration gradient.
When does DNA replication occur
interphase
Explain the importance of mitosis in multicellular organisms
Mitosis can be used to replicate dead cells as the cells are genetically identical. It can be used in an immune response, for example cloning B and T lymphocytes. It can be used in growth as the production of genetically identical cells allows multicellular organisms to arise from zygotes.
Explain the difference in the thickness of the left and right ventricle of the heart
The left ventricle needs to generate more force as the blood is going a further distance all around the body. The right ventricle only needs to develop the pressure to take the blood to the lungs so can be thinner.
How are capillary’s adapted for their function
Their wall is one cell thick meaning that the oxygen does not have to diffuse a long distance. They are very small meaning they can get as close as possible to the respiring cells. Many gaps alow the substance to leave the blood