Plant Hormones Flashcards
All 19 cards in this deck
What is phototropism?
The growth response of a plant to light. Shoots are positively phototropic — they grow towards light.
What is gravitropism (geotropism), and which way do roots and shoots grow?
The growth response of a plant to gravity: roots grow downwards (towards gravity), shoots grow upwards (away from gravity).
What causes a shoot to bend towards the light?
e.g. a seedling lit from one side only
Auxin is unequally distributed, collecting on the shaded side, so cells there elongate more and the shoot bends towards the light.
True or false? In a root lying horizontally, the side with more auxin grows faster.
False. In roots extra auxin slows growth, so the lower side grows less than the upper side and the root bends downwards.
Which plant hormone is important in initiating seed germination?
Gibberellins.
What are the steps to investigate the effect of light on the growth of newly germinated seedlings?
e.g. cress seedlings lit from one side
- Germinate the seeds on damp cotton wool in identical dishes.
- Put one dish in one-sided light (box with a slit), one in all-round light and one in the dark.
- After a few days measure the shoot lengths and record the direction of growth in labelled drawings.
What are the steps to investigate the effect of gravity on newly germinated seedlings?
e.g. germinated bean seedlings laid horizontally
- Pin seedlings onto damp blotting paper in a dish and hold it so the seedlings lie horizontally (A).
- Set up an identical dish rotated on a clinostat as a control (B), so gravity acts equally on all sides.
- Leave both in the dark for 24 hours (so only gravity affects growth), then measure and draw the roots.
Give two control variables for an investigation into the effect of one-sided light on seedling growth.
Any two of: same volume of water, same temperature, same species of plant, same age of seedling.
What are the steps to measure the length of a curved seedling?
e.g. a shoot bent towards a lamp
- Lay a piece of thread along the curve of the shoot.
- Mark the thread level with the tip.
- Hold the thread straight against a ruler and read the length in mm.
(Or straighten the shoot against a ruler, or use a tape measure.)
In required practical 8, in what two ways should the results be recorded?
As length measurements and as careful, labelled biological drawings showing the effects.
Give three commercial uses of auxins.
As weed killers, as rooting powders, and for promoting growth in tissue culture.
Give one disadvantage of using auxin weed killers.
They reduce biodiversity — killing wild broad-leaved plants removes food and habitat for insects and other animals.
Give three uses of gibberellins in horticulture.
To end seed dormancy, to promote flowering, and to increase fruit size.
What is ethene used for in the food industry?
To control the ripening of fruit during storage and transport.
What two processes in plants does ethene control?
Cell division and the ripening of fruits.
True or false? Storing bananas with other fruits makes the other fruits ripen faster.
True. Bananas release ethene, which speeds up the ripening of nearby fruit.
True or false? When investigating the effect of gravity on newly germinated seedlings, the apparatus should be left in the dark.
True. Darkness prevents the direction of light affecting growth (phototropism), so only gravity affects the results.
Why are several seedlings measured and a mean length calculated in the seedling growth practical?
To reduce the effect of random error, giving a more reliable result.
What are the steps to present seedling growth results as a graph?
e.g. mean shoot length recorded each day for 5 days
- Independent variable on the x-axis: time in days
- Dependent variable on the y-axis: mean shoot length in mm
- Plot the points and draw a line of best fit, then describe the trend (e.g. mean length increases with time)