Tissue culture

Gardeners can grow plants from:

• seeds

• cuttings taken from adult plants.

A gardener investigated the growth of roots on cuttings from a geranium plant.

This is the method used.

1. Take 6 cuttings from the stems of the same plant.

2. Prepare 6 test tubes, each containing a different concentration of a solution of chemical Q.

3. Place 1 cutting in each test tube with the cut end of each stem in the solution.

4. Leave the test tubes at room temperature for 10 days.

Figure 8 shows the results.

Tube 1 contains no chemical Q.

Tube 1 is a control.

Why did the gardener include tube 1 in the investigation?

How many times more concentrated is chemical Q in tube 6 than in tube 2 ?

What was the best concentration of chemical Q for stimulating root growth?

Tick (✓) one box.

Give evidence from Figure 8 that a high concentration of chemical Q may be toxic to geranium plants.

The gardener has four types of geranium plant: A, B, C and D.

Plant A produces larger, more brightly-coloured flowers than any of the other plants.

The gardener wants to grow more plants of type A.

Explain why the gardener chooses to take cuttings from plant A instead of growing seeds from plant A.

Reproduction can produce offspring which are:

• genetically different or

• genetically identical.

Farmers grow tomato plants in greenhouses.

The tomatoes are sold in supermarkets.

Suggest one advantage of growing tomato plants that are genetically different.

Suggest one advantage of growing tomato plants that are genetically identical.

Scientists can grow genetically identical tomato plants using tissue culture.

What is tissue culture?

Genetically identical tomato plants growing in the same garden do not all grow to the same height.

Give one reason why.

The sex of dogs is determined by X and Y chromosomes in the same way as in humans.

Complete the Punnett square diagram in Figure 15 to show the inheritance of sex in dogs.

Use the symbols X and Y.

Figure 15

A female dog gave birth to six offspring.

Why would you expect there to be three male offspring and three female offspring?

Use your answer to Question 09.5.

Farmers keep chickens for:

• meat production

• egg production.

Some varieties of chicken grow more quickly and are more suitable for meat production.

Other varieties of chicken produce more eggs.

A farmer keeps two varieties of chicken, A and B.

The farmer investigated the growth rates and egg-production rates of both varieties.

Figure 16 shows the results.

Suggest two control variables the farmer should have used in this investigation.

Figure 16 shows mean values from 500 chickens of each variety.

Give the reason the farmer used a large number of chickens.

The farmer wants to produce a new variety of chicken that is good for both meat production and egg production.

Describe how selective breeding of chicken varieties A and B can produce the new variety of chicken.

Reproduction can produce offspring which are:

• genetically different or

• genetically identical.

Farmers grow tomato plants in greenhouses. The tomatoes are sold in supermarkets.

Suggest one advantage of growing tomato plants that are genetically different.

Suggest one advantage of growing tomato plants that are genetically identical.

Scientists can grow genetically identical tomato plants using tissue culture. What is tissue culture?

Genetically identical tomato plants growing in the same garden do not all grow to the same height. Give one reason why.

The sex of dogs is determined by X and Y chromosomes in the same way as in humans.

Complete the Punnett square diagram in Figure 4 to show the inheritance of sex in dogs. Use the symbols X and Y.

Figure 4

A female dog gave birth to six offspring. Why would you expect there to be three male offspring and three female offspring? Use your answer to Question 03.5.

Farmers keep chickens for:

• meat production

• egg production.

Some varieties of chicken grow more quickly and are more suitable for meat production. Other varieties of chicken produce more eggs. A farmer keeps two varieties of chicken, A and B. The farmer investigated the growth rates and egg-production rates of both varieties. Figure 5 shows the results.

Suggest two control variables the farmer should have used in this investigation.

Figure 5 shows mean values from 500 chickens of each variety. Give the reason the farmer used a large number of chickens.

The farmer wants to produce a new variety of chicken that is good for both meat production and egg production. Describe how selective breeding of chicken varieties A and B can produce the new variety of chicken.

Table 2 gives the classification of four plant species.

Species 1 and 3 are the most closely related.

What information in Table 2 gives evidence for this?

Figure 6 shows the inheritance of flower colour in two species of plant.

• In pea plants and in snapdragon plants, flower colour is controlled by one pair of alleles.

• In Figure 6 the parental generation plants are homozygous for flower colour.

• In heterozygous pea plants, the allele for red flower colour is dominant.

• In heterozygous snapdragon plants, the alleles for flower colour are both expressed.

Use the following symbols for alleles in your answers to Questions 05.2 to 05.4:

Pea plants
Snapdragon plants

R = allele for red flowers C^R = allele for red flowers r = allele for white flowers
C^W = allele for white flowers

What is the genotype of the red-flowered pea plants in the F₁ generation?

What is the genotype of a white-flowered snapdragon plant?

A gardener crossed two pink-flowered snapdragon plants.

Draw a Punnett square diagram to show why only some of the next generation plants had pink flowers.

Identify the phenotypes of all the offspring plants.

What percentage of the offspring would you expect to have pink flowers?

Commercially, hundreds of pink-flowered snapdragon plants can be produced from one pink-flowered plant.

Figure 7 shows a tissue culture technique used for producing many plants from one plant.

Give a reason for each of the following steps shown in Figure 7.

Several groups of cells are scraped off the leaf:

Nutrients are added to the agar jelly:

Hormones are added to the agar jelly:

The plant cells are kept in sterile conditions:

The plant cells are kept at 20^oC:

Explain why the method shown in Figure 7 produces only pink-flowered plants.

Scientists want to breed cows that produce milk with a low concentration of fat.

Figure 10 shows information about the milk in one group of cows.

The cows were all the same type.

In Figure 10 the mean percentage of fat in the milk is equal to the modal value.

Give the mean percentage of fat in the milk of these cows.

A student suggested:

‘The percentage of fat in milk is controlled by one dominant allele and one recessive allele.’

How many different phenotypes would this produce?

Tick one box.

Give the evidence from Figure 10 which shows the percentage of fat in the milk is controlled by several genes.

One of the genes codes for an enzyme used in fat metabolism.

A mutation in this gene causes a reduction in milk fat.

The mutation changes one amino acid in the enzyme molecule.

Explain how a change in one amino acid in an enzyme molecule could stop the enzyme working.

The scientists found one cow with a mutation.

The cow’s milk contained only 2.9% fat.

Figure 11 shows the percentage of fat in the milk of cattle related to the cow with the mutation.

The values for male cattle are the mean values of their female offspring.

Animal 8 is homozygous.

The mutation in animal 7 produced a dominant allele for making low-fat milk.

Give evidence from Figure 11 that animal 7 is heterozygous.

Animals 7 and 8 produced 11 offspring. These offspring were produced by in vitro fertilisation (IVF).

The embryos from IVF were transferred into 11 other cows.

Suggest why IVF and embryo transfer were used rather than allowing animals 7 and 8 to mate naturally.

Draw a Punnett square diagram to show a cross between animals 7 and 8 .

Identify which offspring produce low-fat milk and which offspring produce high-fat milk.

Use the following symbols: D = dominant allele for making low-fat milk d = recessive allele for making high-fat milk

low-fat milk.

The scientists will selectively breed some of the animals shown in Figure 11.

Describe how the scientists would do this.