biology Flashcards
(25 cards)
Explain why antibodies will only bind with specific antigens. (3)
-antibodies have a variable region with a specific primary structure
-tertiary structure of the binding site is complementary to antigen
-forms an antigen-antibody complex
During the immune response, phagocytes present a pathogen’s antigens on their cell surface.
Describe how presentation of antigens leads to the release of antibodies against these antigens. (3)
-helper T cell binds to antigen on the phagocyte
-helper T cell stimulates specific b cell
- b cell divides by mitosis
-to produce plasma cells
Explain how the destruction of T cells by HIV eventually leads to death of the affected individual.
(2)
- T cells cannot active b cells
-the individual is unable to fight off infections
Explain why a high mutation rate makes it difficult to develop a vaccine. (2)
-high mutation rate leads to antigen variability
-vaccines often contain a specific antigen
-antibodies will not be complementary to a changed antigen
Explain how vaccines can be used to protect people against disease.(5)
-vaccines contain antigens
-memory cells are made
-upon second exposure to antigen, memory cells produce antibodies
-antibodies destroy pathogen
Describe the function of the nucleus in non-dividing cells. (4)
-contains genetic material
-contains nucleolus
-makes ribosomes
-contains sequence of bases
Describe how these bacterial cells replicate by binary fission (3)
-replication of DNA
-replication of plasmids
-division of cytoplasm to produce 2 daughter cells
Explain why interfering with the formation of spindle fibres stops the cell cycle. (2)
-chromatids cannot separate on spindle fibres
-so no anaphase
Explain how the behaviour of chromosomes in mitosis results in two genetically identical cells. (6)
Behaviour of chromosomes in prophase:
-chromosomes shorten/thicken/supercoil
-each chromosome is made up of two identical chromatids/strands/copies (due to replication)
Behaviour of chromosomes in metaphase:
-chromosomes/chromatids move to the middle of the cell
OR
chromosomes/chromatids move to the equator
-chromosomes/chromatids attach to individual spindle fibres
Behaviour of chromosomes in anaphase:
-spindle fibres contract
OR
centromeres divide
-(sister) chromatids/chromosomes separate
OR
(sister) chromatids/chromosomes move to opposite poles of the cell
-each pole/end receives identical copies of each chromosome
Behaviour of chromosomes in telophase:
-nuclear envelope forms around each group of chromosomes/chromatids
OR
nuclear envelope forms at each pole
Explain the differences between facilitated diffusion and active transport. (3)
-facilitated diffusion involves channel or carrier proteins while active transport only involves carrier proteins
-facilitated diffusion does not use ATP while active transport uses ATP
-facilitated diffusion takes place down/along a concentration gradient while active transport can occur up/against a concentration gradient
Describe how ester bonds are formed in the synthesis of a phospholipid. (2)
condensation reaction OR reaction involves the loss of water
hydroxyl group OR OH of the glycerol reacts
with the carboxyl group OR COOH of a fatty acid
Individuals with a diet high in glucose can develop high blood pressure. This is due to glucose affecting the volume of blood in the body. Use your knowledge of cell transport to explain how an increase in blood glucose levels could affect blood volume. (3)
glucose lowers the water potential of the blood
water moves into the blood by osmosis (from cells or tissue fluid)
(this) increases the blood volume
Explain how the structure of a triglyceride is related to its function. (3)
insoluble, so does not affect water potential OR does not affect osmosis
long hydrocarbon tails, so bonds can be broken to release energy
low mass to energy ratio, stores lots of energy in a small volume
high ratio of hydrogen to oxygen, so will release water when oxidised
Explain why two individual proteins can have the same number and type of amino acids, but have unique tertiary structures. (2)
different amino acid sequence OR different primary structure
form ionic/hydrogen/disulphide bonds in different places
Describe two differences between the structure of a DNA nucleotide and the structure of an RNA nucleotide. (2)
DNA nucleotides contain thymine, RNA nucleotides contain uracil
DNA contains deoxyribose (sugar), RNA contains ribose (sugar)
Smoking can damage and eventually cause the death of alveolar epithelium cells.
When these cells die, they are replaced by non-specialised and thickened tissue.
Explain why damage to alveolar epithelium cells reduces gas exchange in the lungs. (3)
reduced surface area
increases the diffusion distance
reduces the rate of gas exchange
Describe the pathway taken by a molecule of oxygen from an alveolus to the blood. (2)
across the alveolar epithelium
across the endothelium/epithelium of a capillary
Describe and explain how the action of competitive inhibitors can be reduced in an enzyme-catalysed reaction. (2)
increase the substrate concentration
substrate more likely to bind to active site than competitive inhibitor
Explain how the Golgi apparatus is involved in the digestion of lipids. (3)
modifies/processes triglycerides
combines triglycerides with proteins
packages lipids for release/exocytosis
OR
forms vesicles
Explain how the location of the stomata reduce water loss. (3)
-stomata are sunken
-this traps water vapour
-this reduces water potential gradient
An oxygen concentration gradient is maintained between the alveoli and the lung capillaries.
Describe how ventilation helps to maintain this concentration gradient. (2)
(ventilation) brings in air containing a higher oxygen concentration into the alveoli
(ventilation) removes air with a lower oxygen concentration from the alveoli
The composition of gases within inhaled and exhaled air are different.
Describe how these compositions are different and explain why. (6)
description:
-inhaled air contains more oxygen than exhaled air
-inhaled air contains less carbon dioxide than exhaled air
-inhaled air contains less water vapour than exhaled air
-the relative amount/percentage of nitrogen is different
Explanation (max 3 marks):
-respiration reduces blood oxygen levels OR respiration increases blood carbon dioxide levels
-oxygen enters the blood OR carbon dioxide leaves the blood
by diffusion
water vapour diffuses from moist surfaces
Using the diagram above, describe the structure of HIV. (4)
has RNA as its genetic material
contains enzyme reverse transcriptase
has a protein capsid/capsomeres
has a phospholipid viral envelope
has attachment proteins
Viruses can only replicate once inside host cells.
Describe how HIV replicates inside helper T cells. (4)
RNA is converted into DNA using reverse transcriptase
DNA is inserted into helper T cell
DNA is transcribed into HIV mRNA
HIV mRNA is translated into new HIV proteins (to make new viral particles)
