Common vampire bats [Desmodus rotundus] feed only on blood and die after 70 h of fasting. Unfed bats often receive food from other bats by regurgitation. The graph shows the changes in weight at the time of feeding compared to the pre-feeding weight $(100 \%)$ of donor and recipient bats before and after blood donation.

Using the data, explain blood sharing in vampire bats is an example of the development of altruistic behaviour by natural selection.

The electron micrograph shows human DNA from a cancer cell, showing a stage of DNA replication. The strand of DNA has a replication bubble, where the DNA has unwound into two single strands forming a Y-shaped molecule termed a replication fork. It is here that daughter strands form as the parent DNA acts as a template for the construction of a new matching strand in DNA replication.

(a) Estimate the length of one strand of DNA in the replication bubble.

The electron micrograph shows human DNA from a cancer cell, showing a stage of DNA replication. The strand of DNA has a replication bubble, where the DNA has unwound into two single strands forming a Y-shaped molecule termed a replication fork. It is here that daughter strands form as the parent DNA acts as a template for the construction of a new matching strand in DNA replication.

(b) John Forster Cairns demonstrated by autoradiography that the DNA of bacteria was a single molecule that replicated at two replicating forks (unlike humans that have only one) at which both new DNA strands are being synthesized. Describe Cairns' technique for measuring the length of DNA molecules by autoradiography.

Which pigment traveled the farthest on the chromatography paper?

The picture shows a thin layer chromatogram of an extract of leaves of annual meadow grass (Poa annua). Plastic sheets were coated with silica gel. A drop of extract was spotted at the bottom of the sheet. The sheet was then placed in a beaker of solvent [$75\%$ acetone and $25\%$ petroleum ether].

Identify the most soluble pigment.

The picture shows a thin layer chromatogram of an extract of leaves of annual meadow grass (Poa annua). Plastic sheets were coated with silica gel. A drop of extract was spotted at the bottom of the sheet. The sheet was then placed in a beaker of solvent [$75\%$ acetone and$25 \%$ petroleum ether].

Calculate the $R_f$ for phenophytin. Show your working.

The picture shows a thin layer chromatogram of an extract of leaves of annual meadow grass (Poa annua). Plastic sheets were coated with silica gel. A drop of extract was spotted at the bottom of the sheet. The sheet was then placed in a beaker of solvent [$75\%$ acetone and $25\%$ petroleum ether].

Suggest what would have happened to the pigments of the solvent has been different.

Glass jars containing cultures of chlorella vulgaris microalgae were used as mesocosms. The carbon dioxide released from the combustion of the waste was pumped into the jars to promote photosynthesis and therefore growth of the algae. The jars were kept at $25°C.$ State one other condition required in this mesocosm.

Glass jars containing cultures of chlorella vulgaris microalgae were used as mesocosms. The carbon dioxide released from the combustion of the waste was pumped into the jars to promote photosynthesis and therefore growth of the algae. The jars were kept at $25°C.$ Identify, with a reason, whether this is an open or closed mesocosm.

Glass jars containing cultures of Chlorella vulgaris microalgae were used as mesocosms. The carbon dioxide released from the combustion of the waste was pumped into the jars to promote photosynthesis and therefore growth of the algae. The jars were kept at $25°\mathrm{C}$

One of the jars was kept at a temperature of $30°\mathrm{C}$. Suggest a difference that could be seen in this jar with respect to the rest of the jars.