Tropisms

The body has a hormonal control system that coordinates some of the body’s responses.

The table shows the effects of some of the hormones and the gland that produces each hormone. Complete the table by giving the missing information.

Plants also respond to changes in their environment.

Explain how plants benefit from the responses of their roots and stems to the direction of light they receive.

In many plants, flowering is stimulated by the number of hours of daylight. Suggest why flowering in many plants is stimulated by the number of hours of daylight rather than by temperature.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Tissue culture and plants

In micropropagation, plant tissues are grown in vitro on plant tissue culture media, under aseptic conditions in a controlled environment. This technique is possible because plant cells can differentiate and become specialised cells. This allows them to change their metabolism, growth and development to form a whole plant.

Plant tissue culture media contain substances to support the normal growth and development of plants. The media are mainly composed of minerals, vitamins, and plant hormones. The pH of the media is kept constant.

Plant hormones play an essential role in determining how cells and tissues develop in culture media. Plant cells can differentiate into different tissues and cell types. The concentration of hormones can determine the tissue that develops. Auxins and cytokinins are the most widely used. A balance of both auxin and cytokinin leads to the development of a mass of undifferentiated cells known as a callus.

In vitro cell culture offers an alternative method for conserving endangered species and varieties. Tissue culture can be used when the plant species produce seeds that do not germinate or have seeds that cannot be stored for a long period of time. These can be successfully preserved using in vitro techniques for the maintenance of gene banks.

Embryo culture is a type of plant tissue culture that is used to grow embryos from seeds in nutrient media. In embryo culture, the plant develops directly from the embryo or indirectly through the formation of a callus and then subsequent formation of shoots and roots. The technique has been developed to break dormancy in seeds, and to reproduce rare species and haploid plants.

Scientists are also using cell suspension culture systems from which products can be extracted. A suspension culture is developed by transferring a portion of the callus into liquid media. The media are maintained under suitable conditions of agitation, light and temperature. This system can provide a continuous, reliable source of natural products independent of climate and soil conditions. The first commercial application of large‑scale suspension cultivation of plant cells was carried out to produce shikonin. Shikonin is used in traditional Chinese medicine and is a potential anti‑cancer treatment.

State what is meant by the term in vitro. (line 1)

Explain how plant cells differ from human cells in their ability to differentiate and specialise. (lines 2 and 3)

Give the function of two named minerals included in the culture media. (line 6)

Explain why the pH of the media needs to be kept constant. (line 7)

Auxin also controls the response of plants to light.

Describe a simple experiment you could do to show the phototropic response of plant stems to light.

Explain why scientists want to conserve endangered plant species and varieties. (lines 13 and 14)

Explain why plant cell suspension culture media are maintained under suitable conditions of agitation, light and temperature. (lines 24 and 25)

The following passage is about chemical coordination in animals and plants. Complete the passage by writing a suitable word in the blank space.

Animals and plants use chemicals to coordinate responses. In animals, some glands

produce hormones which are transported in the_........

of the blood. A high glucose concentration in the blood stimulates the release of a

hormone called_........ from

the_........ . This causes an organ called

the_........ to remove glucose from the blood and store it

as a substance called_........ .

Plant shoots grow towards light. This response is

called_........ . The movement of a chemical

called_........ to the shaded side of the shoot causes the

shoot to grow towards the light.

Scientists investigate the effect of salt (NaC l) concentration on the germination of maize seeds.

Batches of seeds are watered with different concentrations of salt solution.

They count the number of seeds that germinate in each batch 12 days after sowing. They then determined the percentage germination.

Describe how the scientists could tell if a maize seed had germinated.

The scientists measured the germination after 12 days.

State two other abiotic variables that the scientists need to control in their investigation.

The table shows the scientists’ results.

Plot a line graph to show the effect of concentration of salt solution on germination.

Use a ruler to join your points with straight lines.

Explain the effect of increasing the concentration of salt solution on germination.

As plants grow, they produce roots and stems.

Compare the responses of roots and stems to gravity.

Compare the responses of roots and stems to light.

The passage describes how plants respond to stimuli. Complete the passage by writing a suitable word in each blank space.

Plant responses to directional stimuli are known as_........ . Plant shoots respond to light coming from one direction by growing _........ the light. This is known as a positive _........ response. It is caused when a plant growth substance called_........ diffuses away from the light. This increases the rate of growth on the side of the shoot furthest away from the light.

Shoots also respond to_........ . This is known as