Lipids

Figure 1 shows the structure of a fatty acid molecule and the structure of a glycerol molecule.

On Figure 1, draw a circle around the part of the fatty acid molecule and the part of the glycerol molecule that is removed to form a bond in a triglyceride molecule.

Name the bond formed between a fatty acid and glycerol in a triglyceride molecule.

Name the reaction involved in forming a bond between a fatty acid and glycerol in a triglyceride molecule.

Table 1 shows information about three fatty acids.

Name the fatty acid shown in Table 1 that is a saturated fatty acid.

The melting point is the temperature at which a solid changes state to be a liquid.

Use Table 1 to describe the relationship between fatty acid structure and fatty acid melting point.

The ratio of saturated to unsaturated fatty acids in a cell-surface membrane determines the extent of the membrane’s fluidity.

Scientists provided a cell culture of mouse phagocytes with liquid broth rich in unsaturated fatty acids.

The scientists observed:

• an increase in the proportion of phospholipids in the phagocytes containing unsaturated fatty acids

• more phagocytosis.

Suggest and explain why there was more phagocytosis.

Write an essay on one of the topics below.

Either

Phosphorus-containing substances and their importance in biological systems.

Or

The mechanisms and importance of transport within organisms.

Describe how a triglyceride molecule is formed.

Table 5 shows some properties of four fatty acids.

Figure 10 shows diagrams of these fatty acids.

Put a tick () in one box that contains correct information about one of these fatty acids.

The percentage of saturated fatty acids compared with unsaturated fatty acids found in lipid stores in seeds differs in different populations.

Scientists investigated two populations of the plant, Helianthus annuus.

The scientists grew young plants from seeds collected from each population. They placed the seeds on wet tissue paper so that the root growth was visible.

They grew seeds from each population at two temperatures:

• warm temperature of 24 °C

• cool temperature of 10 °C

After 10 days, the scientists measured the length of each root.

Table 6 shows some of the properties of the two populations and the scientists’ results.

The mean ±2 × standard deviation includes 95% of the data.

The scientists used a data logger to measure the length of the root rather than a ruler.

Suggest one reason why they used a data logger and explain why this was important in this investigation.

It is known that:

• during respiration saturated fatty acids yield more energy than unsaturated fatty acids

• saturated fatty acids have higher melting points than unsaturated fatty acids

• lipases in seeds act more rapidly on liquid substrates.

Use this information and Table 6 to show how each population is better adapted for its natural environment when compared with the other population.

Although these two populations are completely separate and show genetic variation, they are both called Helianthus annuus.

Explain why they are both given this name.

Complete Table 7 with ticks () to show which elements are found in the following biological molecules.

After Watson and Crick proposed the model of DNA structure, scientists investigated

the possible mechanisms for DNA replication.

Two scientists grew a bacterial population, providing them with a nitrogen source containing only the heavy isotope of nitrogen,¹⁵ N. As soon as all the DNA in this population contained¹⁵ N, the scientists changed the nitrogen source to one containing only the lighter isotope of nitrogen,¹⁴ N. They changed the nitrogen source at 0 hours.

During the investigation, the scientists measured the size of the population of bacterial cells.

Figure 11 shows the scientists’ results.

The generation time for a population of bacteria is the time taken for all the bacteria to divide once by binary fission.

Use Figure 11 and the following equation to calculate the generation time for this population of bacteria. Give your answer in hours.

size of population at time 4 hours

At intervals during this investigation, the scientists removed samples of the bacterial population, isolated the DNA and measured the density of the DNA.

DNA made using¹⁵ N has a higher density than DNA made using¹⁴ N.

Figure 12 shows the scientists’ results.

There are three possible models of DNA replication.

These models are shown in Figure 13.

Which of these models, P, Q or R, is supported by the results shown in Figure 12 ?

Give the letter and name of the model supported and explain why the results do not support the other models.

Explanation for first unsupported model

Explanation for second

Explain five properties that make water important for organisms.

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.

Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers.

Give two named examples of polymers and their associated monomers to illustrate your answer.

Describe the gross structure of the human gas exchange system and how we breathe in and out.

Mucus produced by epithelial cells in the human gas exchange system contains triglycerides and phospholipids.

Compare and contrast the structure and properties of triglycerides and phospholipids.

Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose, attached.

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.