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- Identify and draw, using a hand lens if necessary, the sepals, petals, stamens, filaments and anthers, carpels, style, stigma, ovary and ovules, of an insect-pollinated flower
Here’s a diagram of a typical dicot, insect-pollinated flower:
Just so that you get a better idea of how these parts actually look in real life (which would probably be a good idea if you’re writing the practical exam) it’s a good idea to pluck an actual dicotyledonous flower and compare its parts to the ones given on the diagram. Cut it up and dissect it, if it’ll help you identify all the parts.
If you’re confused as to whether the flower is insect-pollinated or not, if it has petals, it’s probably insect pollinated. If you don’t know whether it’s dicot or monocot, the leaves on dicotyledonous plants tend to be veiny, and the veins branch out towards the edges of the leaf.
- Use a hand lens to identify and describe the anthers and stigmas of a wind-pollinated flower
Wind-pollinated flowers are different in structure because they do not have to attract insects to them but do need to be exposed to the wind.
- The sepals are a hard layer that protect the flower while it is a bud.State the functions of the sepals, petals, anthers, stigmas and ovaries
Petals come in different, often vibrant, colours to attract insects for pollination.
Anthers contain pollen sacs. This is where pollen grains are formed. Pollen grains contain the male gametes (sex cells) required for fertilisation.
The stigma is a sticky surface that catches the pollen during pollination.
The ovaries contain ovules. These develop into seeds when they are fertilised.
- Distinguish between the pollen grains of insect-pollinated and wind-pollinated flowers
Pollen grains from insect-pollinated flowers are larger and heavier than grains from wind-pollinated flowers.
Insect-pollinated flowers have pollen grains that are usually either sticky or spiky – this helps the pollen get stuck to insects, assisting the pollen in getting carried to another flower.
Wind-pollinated flowers have smooth and light pollen grains so that the wind can carry the pollen to other flowers without the pollen clumping together.
Wind-pollinated flowers also produce higher numbers of pollen grains than insect-pollinated flowers.
- Define pollination as the transfer of pollen grains from the anther to the stigma
Pollination is the transfer of pollen grains from the anther to the stigma
- Name the agents of pollination
Animals, including insects; the wind; water.
- State that fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule
Fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule.
- Describe the structural adaptations of insect-pollinated and wind-pollinated flowers
- Investigate and state the environmental conditions that affect germination of seeds, limited to the requirement for water, oxygen and a suitable temperature
Before telling you the required environmental conditions, it’ll be useful for you to know the basic structure of the seed.
The tough outer coat is called the testa. The cotyledon serves as a food store. The radicle grows to become a root, and the plumule grows to become a shoot. According to Cambridge, the radicle, plumule, and cotyledons are all part of the embryo.
Seeds mostly require three environmental conditions for germination: oxygen, water and growth.
Oxygen is required for respiration, which provides the seed with the energy necessary for germination.
Water is required to make the food in the food stores of the seed soluble so that they can be transported to the seed embryo and used in respiration. It is also required for the seed to swell and burst so that the root and shoot can emerge.
Most seeds require warmth to germinate, which is why most plants only grow in spring and summer.
Investigating these conditions:
First, I’ll describe the investigation of temperature:
Take five or more transparent containers. Stuff them with kitchen tissue and spray adequate water in each (so that the tissue in each container is damp, but not a soggy a mess). Put the same number of seeds in each container (e.g. four seeds in each), making sure that each of the seeds are visible from outside the container. Make sure the containers are open to the air, so plenty of oxygen reaches each seed.
Place each of the containers in different incubators at different temperatures, for three weeks. Maintain the dampness of the tissue in each container for the duration of the experiment. Take pictures of the containers (so that we can view all the seeds) at the same time each day, every day for three weeks. Note which seeds sprout the fastest, and which temperature they germinate at. You will notice that the seeds at warmer temperatures sprout faster, but if the temperature is too high or low, they end up not sprouting.
To investigate water:
Use two transparent containers stuffed with tissue, and place the same number of seeds in each. Make sure that there are enough air spaces for each seed to receive plenty of oxygen. Spray one of the containers with water, and leave the other one dry.
Place the two containers in two different incubators for three weeks, at the same temperature (25oC). Take pictures every day, at the same time of day, throughout the experiment and note which seeds germinate.
Investigating oxygen:
Use two transparent containers. Fill one with wet sand (this will reduce the air supply to the seeds in this container greatly), and set up the other with damp tissue. Place seeds in each so that they are visible from outside the container. Incubate both containers at the same temperature for three weeks, taking pictures every day at the same time of each day. Note which seeds germinate first.
Notes submitted by Sarah
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