AQA Biology__4_5_6 markers Flashcards
Describe how the structures of starch and cellulose molecules are related to their functions.
Starch has a helical/spiral shape, is large and insoluble making it osmotically inactive, is branched for easy glucose release for respiration, and is large so cannot leave the cell. Cellulose consists of long, straight/unbranched chains of β-glucose, joined by hydrogen bonding, forming microfibrils that provide rigidity/strength.
Compare and contrast the structure and properties of triglycerides and phospholipids.
Both contain ester bonds and glycerol, and fatty acids may be saturated or unsaturated. Both are insoluble in water and contain C, H, and O, but phospholipids also contain P. Triglycerides have three fatty acids, while phospholipids have two fatty acids plus a phosphate group. Triglycerides are hydrophobic/non-polar, whereas phospholipids have hydrophilic and hydrophobic regions. Phospholipids form micelles in water, but triglycerides do not.
Describe how lactose is formed and where in the cell it would be attached to a peptide to form a glycoprotein.
Lactose is formed from glucose and galactose joined by a condensation reaction through a glycosidic bond. It is added to a polypeptide in the Golgi apparatus.
Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar, and amylase in a sample.
For lipids, add ethanol and then water, shaking to form a white milky emulsion. For non-reducing sugars, perform Benedict’s test which stays blue, then boil with acid, neutralize with alkali, and heat with Benedict’s to form a brick-red precipitate. For amylase, add biuret reagent which becomes lilac, then add starch and test for the presence of starch.
Describe how an ATP molecule is formed from its component molecules.
An ATP molecule is formed from adenine, ribose (pentose), and three phosphates through a condensation reaction, facilitated by ATP synthase.
Describe the process of semi-conservative replication in DNA.
DNA helicase breaks hydrogen bonds causing the DNA to unwind. Both strands act as templates. Free DNA nucleotides line up in complementary pairs (A-T, G-C). DNA polymerase joins the nucleotides, forming phosphodiester bonds. Each new DNA molecule consists of one old template strand and one new strand.
Describe the structure of DNA.
DNA is a double helix composed of two strands of nucleotides, with a sugar-phosphate backbone and nitrogenous bases (adenine, thymine, cytosine, guanine) paired in specific combinations (A-T and C-G).
What joins the nucleotides during DNA replication?
Polymerase joins the nucleotides.
What type of bonds are formed between nucleotides in DNA?
Phosphodiester bonds.
What does each new DNA molecule consist of?
One old template strand and one new strand.
What is the structure of DNA?
DNA is a polymer of nucleotides.
What are the components of each nucleotide in DNA?
Each nucleotide is formed from deoxyribose, a phosphate, and an organic base.
What type of bonds hold the two strands of DNA together?
Hydrogen bonds.
What base pairs with adenine in DNA?
Thymine (A-T) and guanine pairs with cytosine (G-C).
What is the process of translocation in plants?
Sucrose is actively transported into the phloem/sieve tube element.
What cells are involved in the translocation of sucrose?
Companion cells.
What effect does sucrose transport have on water potential?
It lowers the water potential in the sieve tube element/phloem.
What pressure is produced during translocation?
High hydrostatic pressure.
What drives the mass flow of substances in translocation?
Mass flow towards the sink for storage.
What happens to sugars at the sink during translocation?
The sugars are unloaded.
What is the cohesion-tension theory of water transport in the xylem?
Water is lost from the leaf by transpiration.
What happens to the water potential of mesophyll cells during transpiration?
It lowers the water potential.
How do water molecules behave in the xylem?
Water molecules cohere by hydrogen bonds.
What is formed as a result of water cohesion in the xylem?
A continuous column of water.
What is the role of iron ions in cells?
Haemoglobin binds with oxygen.
What is the role of sodium ions in cells?
Co-transport of glucose and amino acids into cells.
How does sodium affect water potential?
It creates a sodium concentration gradient.
What is the role of phosphate ions in cells?
Joins nucleotides in the phosphodiester backbone of DNA/RNA.
What are five important properties of water for organisms?
- A metabolite in various reactions. 2. A solvent for metabolic reactions. 3. High specific heat capacity. 4. Large latent heat of vaporization. 5. Cohesion supports continuous columns of water.
What reaction joins monomers to form polymers?
A condensation reaction.
What reaction breaks polymers into monomers?
A hydrolysis reaction.
What are two examples of polymers and their associated monomers?
DNA - nucleotides; Lactose - glucose & galactose.
What bonds are involved in forming polymers?
Glycosidic, ester, and phosphodiester bonds.
How is mRNA formed by transcription in eukaryotes?
Hydrogen bonds between DNA bases break.
What strand acts as a template during transcription?
Only one strand of DNA.
How do free RNA nucleotides align during transcription?
By complementary base pairing.
What base replaces thymine in RNA?
Uracil.
What enzyme joins adjacent RNA nucleotides?
RNA polymerase.
What bonds are formed between adjacent RNA nucleotides?
Phosphodiester bonds.
What happens to pre-mRNA after transcription?
It is spliced.
How is mRNA formed by transcription in eukaryotes?
- Hydrogen bonds between DNA bases break.
- Only one strand acts as a template.
- Free RNA nucleotides align by complementary base pairing.
- Uracil binds with adenine (replaces thymine).
- RNA polymerase joins adjacent RNA nucleotides.
- By forming phosphodiester bonds.
- Pre-mRNA spliced to form mRNA (introns removed).
How is a polypeptide formed by translation of mRNA?
- mRNA attaches to ribosomes (RER).
- tRNA anticodons bind to complementary mRNA codons.
- tRNA brings a specific amino acid.
- Amino acids join by peptide bonds.
- With the use of ATP.
- tRNA released.
- The ribosome moves along the mRNA to form the polypeptide.
How does the structure of glycogen relate to its function?
- Coiled so compact.
- Polymer of glucose so easily hydrolysed.
- Branched so more ends for quick hydrolysis.
- Insoluble so not easily lost from cell, doesn’t affect water potential.
How does translation lead to the production of a polypeptide starting with mRNA in the cytoplasm?
- mRNA associates with a ribosome.
- Ribosome moves to the start codon.
- tRNA brings an amino acid.
- Anticodon complementary to codon.
- Ribosome moves along to next codon (can fit 2 tRNAs).
- Process repeated and amino acids join by peptide bonds in a condensation reaction - using energy from ATP.
How is mRNA produced in a plant cell?
- The DNA strands separate by breaking H bonds.
- Only one strand is used as template.
- Complementary base pairing (A&U, T&A, C&G).
- RNA nucleotides joined by RNA polymerase.
- Pre-mRNA formed.
- Introns spliced to form mRNA.
How does the structure of a protein depend on the amino acids it contains?
- Structure is determined by relative position of amino acid R group.
- Primary structure is order of amino acids.
- Secondary structure formed by hydrogen bonding between amino acids.
- Tertiary structure formed by interactions between R groups.
- Creates an active site in enzymes.
- Quaternary structure contains more than one polypeptide chain.
Contrast how an optical microscope and a transmission electron microscope work and their limitations.
- TEM uses electrons and optical uses light.
- TEM allows greater resolution.
- With TEM, smaller organelles can be seen/greater detail.
- TEM views only dead specimens and optical can view live specimens.
- TEM doesn’t show colour, optical does.
- TEM requires thinner specimens.
- TEM requires a more time-consuming, complex preparation.
- TEM focuses using magnets while optical uses glass lenses.
How could you estimate the size of a population of sundews in a small marsh?
- Use a grid.
- Use a calculator to generate random numbers.
- Count frequency in a quadrat.
- Obtain a large sample of at least 20 and calculate the mean.
- Mean number of quadrats per m² multiplied by m² in total field.
How can you estimate the size of a population of sundews in a small marsh?
- Use a grid
- Use a calculator to generate random numbers
- Count frequency in a quadrat
- Obtain a large sample of at least 20 and calculate the mean.
- Mean number of quadrats per m² multiplied by m² in total field.
Explain the mark-release-recapture method for estimating fish population size.
- Capture/collect sample, mark and release
- Ensure marking is not harmful to fish and doesn’t affect the survival chances of the fish.
- Allow time for fish to randomly distribute before collecting a sample
- Population = no. of fish in first sample x no. in second sample / no. of fish recaptured.
How do two species of palm tree arise via sympatric speciation?
- Occurs in the same habitat
- Mutations cause different flowering times
- Reproductive isolation
- Change in the frequency of alleles
- Disruptive selection
- Eventually, the two species cannot interbreed to produce fertile offspring.
Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells.
- Nucleotide structure is identical
- Nucleotides joined by phosphodiester bonds
- Eukaryotic DNA is longer
- Eukaryotic DNA contains introns, prokaryotic doesn’t
- Eukaryotic DNA is linear, prokaryotic is circular.
- Eukaryotic DNA associated with histones, prokaryotic isn’t.
