✅ 8. Required Practical: Investigating Newly Germinated Seedlings (B11) Flashcards
Aim Of The Practical
In this practical you will plan and carry out an experiment to investigate how light affects the growth of newly germinated seedlings.
Safety Measures for this Practical
- Take care when using scissors
- Wash hands after handling compost
- Be aware of any students with relevant allergies.
Equipment for this Practical
- Newly germinated seedlings, for example, cress, rapid-cycling Brassica rapa (fast plants), Sinapis alba (white mustard), Raphanus sativus (radish)
- Two Petri dishes
- Cotton wool or compost
- Water and pipette
- Small cardboard box (e.g. shoebox)
- Scissors
- Lamp or a light bank
- Ruler
- String
How To Control The Variables
Number of Seeds - Use the same number of seeds in each dish
Type of Seed - Use seeds that all come from the same packet
Temperature - Keep your Petri dishes in a place where the temperature is stable (i.e away from heat sources and draughts)
Water - Use a measuring cylcinder to add the same amount of water
Light Intensity - Keep the distance between bulb and the dish the same
Method for this Practical
- You will be given three Petri dishes each containing five newly geminated seedlings growing in a layer of cotton wool or compost.
- Measure the length of each shoot. Measure from the base of the shoot to the tip. Write your measurements in your results table, and ensure each Petri dish has the same number of germinated seedlings that will grow.
- Number the shoots and identify which shoot is which before you move your Petri dishes in different places
- Place one of the Petri dishes inside the box, meaning it will recieve no light at all. Place another directly under a lamp, so the light intensity on the seedlings is high, and place the other petri dish is a dark corner of the room, so it only recieves ambient light.
- Make sure you come back regularly to measure the growth and appearance of the seddlinsg while the grow. You will also need to add water during this time to make sure that the cotton wool or compost stays moist but not waterlogged.
- After about a week, measure the length of each shoot. Measure from the base of the shoot to the tip. If a shoot is curved, straighten it before you measure it, or use a piece of string to mark off its length and then measure the string. Write your measurements in your results table.
- Take the careful measurements and input them into the results table, and then draw up a graph of your results.
Hypothesis for this Practical
My hypothesis for this experiment is that the seedlings placed in the dark will actually grow the most. This is due to the fact that when seeds usually germinate underground, they grow rapidly in order to reach the light, so if the seedlings are kept in the dark, then they will continue to grow rapidly to trying and reach any light that they think is above the surface.
Independant Variable for this Practical
The Independant Variable in this experiment is the light intensity (where there’s no light, a little light, and lots of light). This is because it is the variable that this changed and altered to affect the dependant variable in this test.
Dependant Variable for this Practical
The Dependent Variable in this experiment is the seedling height (and even direction and colour). This is the dependant variable because it is the variable that is being tested/measured in this experiment.
Control Variables for this Practical
The Control Variables in this experiment are the number of seeds, type of seeds, temperature, water, and light intensity. These are control variables because they have to stay the same throughout the experiment to ensure that it is kept as a fair test.
a) What term is used to describe a growth movement in plants?
b) What chemicals control growth movements in plants?
c) What is the name of the hormone that controls photostrophism and gravitropism?
a) Tropism
b) Hormones
c) Auxin
What would be a good way of negating gravity (or proving that gravity is the deciding factor in direction of plant growth)?
To negate gravity, a clinostat can be used. A clinostat is a device which uses rotation to negate the effects of gravitational pull on plant growth (gravitropism) and development (gravimorphism). This will result in the plant growing in a horizontal direction, therefore proving that gravity is a deciding factor in the direction of plant growth.
Why are the Leaves on the plant left in the Dark Small and Yellow?
The seedlings left in the dark turn small and yellow due to the fact that once the seedlings have used all of their energy stores, they cannot carry out photosynthesis in the dark.
What can you conclude about the effect of the independant variable (light exposure) on the length of the seedlings
I can conclude that the less light exposure the seedlings recieve, the more they will grow.
(While their leaves will also be less green, and more yellow)
What is the scientific reasoning for the plants in less light to grow more
The reasoning for this is that the auxin collects on the shaded side away from any light (which is the bottom of the plant in this scenario). This causes increased cell growth/elongation in the plant as a result.
What are 2 control variables in this experiment
The medium the seeds are placed in must be the same, and the temperature the seeds are stored at should be kept equal.
Why is it neccessary to control certain variables
Controlling these variables is neccessary, due to the fact that if one set of seedlings are different, or stored in hotter conditions, then they’d be disporportionately advanatges than the other sets of seedlings, skewing the results. This shows the differences in growth are due to the factors being tested, and nothing else.
Why is more than one seedling used in under the seperate conditions?
More than one seedling was used to obtain more data from repeatable results. As a result, a mean average can be found, which increased the reliability of the results.
How could the experiment be improved
One way that this experiment could be improved is through using more seedlings, so the experiment can be repeared more. This in turn will obtain more data, which will then improve the accuracy of the mean average, improving the accuracy of the experiment.
What two ways can this experiment be extended to do further investigations?
One way I could extend my experiment is by putting another set of seedlings in a box with a hole cut out on the side of it, which would measure how plant growth is affected by the direction of light. Another way the experiment could be extended is by testing the effect of gravity on germinating seedlings. This could be done by placing a plant on it’s side and seeing which direction it grows and curves in (or a clinostat could be used to show how when the direction of gravity is constantly changing, the plant grows in a horizontal line)
Give 1 safety consideration you should take into account in this experiment
Wash your hands after handling the compost or the seedlings to avoid any risks of infection.
Describe and Explain the results found in this experiment
Under intense light conditions, the seedlings grew the least over the 6 days. This would’ve been due to the fact that the seedlings were fully immersed in light. This means that less auxin would’ve built up at the bottom of the plant, as auxin builds up on the shaded sides of plants, meaning a plant fully surrounded with light wouldn’t experience this benefit.
In ambient, the seedlings grew the second most, which will be down to the fact that there are some shaded areas of the plant where auxin will be allowed to build up in, meaning that the growth/elongation of cells in that area will be increased, meaning these seedlings will grow taller.
Finally, in no light, there are lots of shaded areas, meaning lots of auxin will accumate in the plant’s stem. This results in more growth and elongation of the cells in these plants than the other ones, due to the increased auxin levels. As a result of this, these seedlings will grow the tallest out of all of them, proving the effect of light on the growth of plants.
