It starts with a seed: Germination
Germination is the process in which a seed develops into a new plant. Most seeds cannot begin to germinate until they have access to water.
There are three stages to germination:
1.The seed takes in water through a process known as imbibition. This causes the seed to swell and break the seed coat.
2.The water activates enzymes within the seed. These enzymes break down the seed’s food store to produce energy for growth.
3. The radicle (the embryonic root) leaves the seed and grows down into the soil. The plumule (the embryonic shoot) emerges shortly after and grows upwards, out of the soil.
1.The seed takes in water through a process known as imbibition. This causes the seed to swell and break the seed coat.
2.The water activates enzymes within the seed. These enzymes break down the seed’s food store to produce energy for growth.
3. The radicle (the embryonic root) leaves the seed and grows down into the soil. The plumule (the embryonic shoot) emerges shortly after and grows upwards, out of the soil.
What do plants need for growth?
Plants require a certain number of conditions for growth. These include:
- Sunlight – Plants require sunlight to perform photosynthesis (the process through synthesise food). For this reason, plants cannot grow in the dark, and even artificial, indoor light, will usually not be enough for plants to grow well.
- Water – Just as seeds need water to begin germination, plants also require water to carry out their life processes. Plants absorb water through their roots, and then use special tissues to transport the water to all parts of the plant, including the topmost leaves. However, too much water can prevent the roots from absorbing the nutrients they need.
- Nutrients – Plants absorb nutrients from the soil through their roots. The many different nutrients that plants require are divided into micronutrients and macronutrients. Micronutrients are required in small quantities, while macronutrients are required in small amounts. There are at least twenty essential nutrients required plants, including nitrogen, phosphorous and potassium.
- Air – Plants absorb both oxygen and carbon dioxide from the air through the stomata on their leaves. Oxygen is required for respiration, while carbon dioxide is required for photosynthesis.
- Soil – Healthy soil is also a requirement for the growth of most plants. In order for the soil to be healthy, it should have both organic (such as decaying leaves) and inorganic matter (small pieces of rock), along with water and air. The acidity of the soil is also important, as plants cannot grow if soil is too acidic.
Plants have hormones too!
Plant growth and development is controlled by plant hormones known as gibberellins. While gibberellins cause plant cells to elongate and grow taller, they are also responsible for stimulating processes such as germination, flowering and fruit ripening. These hormones are produced in the seeds, roots, stem and young leaves of the plant.
Tropism
Tropism is a plant’s response to a stimulus. Negative tropism occurs when a plant grows away from a stimulus, while positive tropism occurs when a plant grows towards a stimulus.
Phototropism
[Photo means light]
Phototropism occurs when plants grow towards or away from sunlight. As sunlight is essential for plant growth, most plants exhibit positive phototropism, meaning they grow towards sunlight.
Phototropism
[Photo means light]
Phototropism occurs when plants grow towards or away from sunlight. As sunlight is essential for plant growth, most plants exhibit positive phototropism, meaning they grow towards sunlight.
Gravitropism or Geotropism
[Gravi refers to gravity]
Gravitropism occurs when plants grow in the direction of gravity, or in the opposite direction of gravity. Plant shoots exhibit negative gravitropism as they grow upwards, against gravity. Plant roots exhibit positive gravitropism as they grow downwards, with gravity. This positive gravitropism is beneficial to roots as they must grow downwards to find nutrients and water in the soil, while leaves will find more available light when they grow upwards.
[Gravi refers to gravity]
Gravitropism occurs when plants grow in the direction of gravity, or in the opposite direction of gravity. Plant shoots exhibit negative gravitropism as they grow upwards, against gravity. Plant roots exhibit positive gravitropism as they grow downwards, with gravity. This positive gravitropism is beneficial to roots as they must grow downwards to find nutrients and water in the soil, while leaves will find more available light when they grow upwards.
Thigmotropism
[Thigmo comes from the Greek word thigma meaning to touch]
Thigmotropism occurs when plants grow in response to touch. This is seen most often in the tendrils of peas or Morning Glory. Thigmotropism allows plants to attach to supports in order to climb up or along surfaces. (see picture)
Hydrotropism
Using you knowledge of prefixes such as photo-, gravi- and thigmo-, what do you think hydrotropism is? Write you own definition for this word. (K/I)
[Thigmo comes from the Greek word thigma meaning to touch]
Thigmotropism occurs when plants grow in response to touch. This is seen most often in the tendrils of peas or Morning Glory. Thigmotropism allows plants to attach to supports in order to climb up or along surfaces. (see picture)
Hydrotropism
Using you knowledge of prefixes such as photo-, gravi- and thigmo-, what do you think hydrotropism is? Write you own definition for this word. (K/I)
What Controls Tropism?
Auxins are the plant hormones that control phototropism and gravitropism. They are produced at the tips of roots and shoots, and are moved to other parts of the plant when necessary. Auxins are destroyed by light, so when a plant is exposed to sunlight from one direction, the auxins on the 'light' side are destroyed, but the auxins on the ‘shaded’ side are still intact. The auxins diffuse down the ‘shaded’ side and cause the plant cells on this side to elongate, causing the plant to bend towards the light.
Observe the experiment below
A – The tips of the shoots were cut off
B – Foil caps were placed on the tips of the shoots
C – The shoots were allowed to grow normally
Please answer the following questions:
B – Foil caps were placed on the tips of the shoots
C – The shoots were allowed to grow normally
Please answer the following questions:
- What phenomenon is being demonstrated? What controls this? (K/U/T/A)
- Why are the ‘A’ plants not as tall as the ‘B’ and ‘C’ plants? (U/A)
- Why are the ‘B’ plants growing straight upwards? (U/A)
Watch the video and answer the following questions
- On what day do we see the plumules for the first time? (K/U)
- In days 1 and 2, it does not appear as though the seeds are growing at all, but of course, we know they are growing. What is happening? Describe what you think is happening inside the seed during these days. (K/U/T)
- Observe the branching roots developing in days 5 and 6. (K/U/I)
- What is the benefit of this type of growth?
- Why do the roots grow downwards instead of upwards?
- Which plant hormones aid the plant in this growth?
- In day 8 you can see that the plants are bending away from the camera, towards the window. Why are the plants growing like this? Name this process and describe how it works. (K/U/T/A)
Have you ever wondered what plants sound like?
Before watching this video:
If plants could make sounds, what type of sounds do you think they would make? Write down a genre of music or a specific song that you think would best represent plant sound.
If plants could make sounds, what type of sounds do you think they would make? Write down a genre of music or a specific song that you think would best represent plant sound.
Finally...
Design an experiment to test hydrotropism or thigmotropism. You could design an experiment to test gravitropism/geotropism, as long as it is different from the that in the picture.
Make sure you think about what is required for your seeds to germinate, and the different conditions that your plants will need to grow.
Make sure you think about what is required for your seeds to germinate, and the different conditions that your plants will need to grow.
Sources
BBC Bitesize. Phototropism and Auxin. Retrieved March 28, 2016, from http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/growth_development/singlecellrev4.shtml
Boundless. “Plant Responses to Gravity.” Boundless Biology. Boundless, 08 Jan. 2016. Retrieved 28 Mar. 2016 from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/plant-form-and-physiology-30/plant-sensory-systems-and-responses-184/plant-responses-to-gravity-703-11928/
Boundless. “Plant Responses to Light.” Boundless Biology. Boundless, 08 Jan. 2016. Retrieved 28 Mar. 2016 from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/plant-form-and-physiology-30/plant-sensory-systems-and-responses-184/plant-responses-to-light-700-11925/
Farabee, M. J. (n.d.). PLANT HORMONES, NUTRITION, AND TRANSPORT. Retrieved March 28, 2016, from https://www2.estrellamountain.edu/faculty/farabee/BIOBK/BioBookPLANTHORM.html
BBC Bitesize. Phototropism and Auxin. Retrieved March 28, 2016, from http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/growth_development/singlecellrev4.shtml
Boundless. “Plant Responses to Gravity.” Boundless Biology. Boundless, 08 Jan. 2016. Retrieved 28 Mar. 2016 from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/plant-form-and-physiology-30/plant-sensory-systems-and-responses-184/plant-responses-to-gravity-703-11928/
Boundless. “Plant Responses to Light.” Boundless Biology. Boundless, 08 Jan. 2016. Retrieved 28 Mar. 2016 from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/plant-form-and-physiology-30/plant-sensory-systems-and-responses-184/plant-responses-to-light-700-11925/
Farabee, M. J. (n.d.). PLANT HORMONES, NUTRITION, AND TRANSPORT. Retrieved March 28, 2016, from https://www2.estrellamountain.edu/faculty/farabee/BIOBK/BioBookPLANTHORM.html