The Natural World Series Written and performed by Stephanie Poppins This sleep series has been written to provide an educational transition into deep sleep.
Having taught in high schools for over 20 years,
I have come to understand learning happens in a myriad of ways,
And sometimes when you least expect it.
It is my pleasure to present to you one of those ways.
But before we begin,
Let's take a moment to focus on where we are now.
Take a deep breath in through your nose,
And let it out on a long sigh.
It is time to relax and fully let go.
Feel your shoulders melt away from your ears,
And feel yourself relaxing to the support beneath you,
As you let all the worries of the day seep away.
You are safe here.
We are all safe here.
Happy listening.
Episode 4 Plant Processes Episode 4 Plant Organisation The main role of plants,
Stems and roots are to transport substances around the plant.
They have two types of transport systems,
Xylem and phloem.
Xylem transports water and minerals,
And phloem transports sugars and amino acids dissolved in water.
These are distributed differently in roots and stems.
In the root of a plant,
The xylem forms a central column,
A solid support.
The phloem is towards the centre,
Outside the xylem.
In the stem,
The transport tissues of the xylem tubes are grouped into vascular bundles.
Any part of a plant above ground where it is exposed to light can photosynthesise.
But a plant's leaves are the main organ of photosynthesis.
Plant leaves are adapted for gas exchange and photosynthesis.
Each leaf has a large surface area for maximum absorption of light and for optimum absorption of carbon dioxide.
It is a thin,
Flattened blade,
Although there are exceptions,
So that water and gases have a limited distance to diffuse.
Branches of the xylem tubes transport water and minerals to the leaf.
Branches of the phloem tubes transport the glucose and the other products of photosynthesis to other parts of the plant.
Plant leaves are adapted for photosynthesis and the exchange of gases required for the process.
The structure of the tissues is always related to their functions within the plant.
In order to absorb the light energy from the sun,
The palisade mesophyll layer of the leaf is adapted.
The cells are packed with many chloroplasts.
They are column-shaped and arranged closely together towards the upper surface of the leaf.
Spongy mesophyll tissue is packed loosely for efficient gas exchange.
These cells are covered by a thin layer of water and gases dissolve in this water as they move in and out of the cells.
When a plant is photosynthesising during the day,
These features allow carbon dioxide to diffuse into the spongy mesophyll cells and oxygen to diffuse out of them.
To enter the leaf,
Gases diffuse through small pores called stomata.
As the stomata open,
Water is lost by the process of transpiration.
Closing the stomata helps to control water loss.
The xylem and phloem tubes are a way of transporting chemicals throughout the leaf.
The xylem transports water and minerals from the roots up the plant stem and into the leaves.
In a mature flowering plant or tree,
Most of the cells that make up the xylem tubes are specialised cells called vessels.
The phloem tubes move food substances the plant has produced by photosynthesis to where they are needed.
Growing parts of the plant need them.
Storage organs such as bulbs and tubes and developing seeds need them too.
Transporting the phloem tubes is therefore both up and down the stem.
So we can see,
As plants need to take up water,
Minerals and carbon dioxide and transport them to the leaves,
They must have the xylem tubes.
To move the products of photosynthesis to where they are needed in the plant,
The plant needs to have phloem tubes.
As the size of the plant increases,
The surface area in relation to their volume decreases.
In a larger organism,
The substance will also have further to travel in order to diffuse.
Larger plants and animals need transport systems and to ensure that they have sufficient absorbing surface area.
This could be additional surfaces such as the digestive system and lungs in animals,
Or adaptations such as the flattened shape of leaves in plants which increase their surface area.
As water is lost through the leaves from diffusion,
Water is drawn from the cells in the xylem tubes to replace that.
As this water travels through the tubes in the stem of the leaf,
It is then replaced by water taken up by the roots.
This process is called transpiration.
But only 5% of the water taken up by the plant is used for photosynthesis.
The water is also used to cool the leaf as water evaporates.
It keeps the cells turgid,
Which supports herbaceous plants.
The water uptake in the roots is made possible through fine root hairs,
Which are single-celled extensions of epidermal cells in the root.
They grow between soil particles and absorb water and minerals from the soil.
Water enters the root hair by a process of osmosis.
This happens because soil water has a higher water potential than the cytoplasm of the root hair cell.
Minerals as well enter the roots by active transport.
Soil water moves into the root hair cell by osmosis and across the root to the xylem tubes,
Which is then carried up through the stem into the leaves.
The rate of transpiration is affected by several factors.
These include the temperature which the plant finds itself in,
The humidity in the air and the movement in the air,
The intensity of light.
All of these have to be factored in when looking at the rate of transpiration.
The temperature increase will also increase molecular movement so that more water molecules evaporate from cell surfaces.
The rate of diffusion,
Therefore,
From the leaf is increased.
Lack of air humidity would reduce the concentration of water molecules outside the leaf and so the diffusion of water from the leaf will increase.
Air movement increase will remove water vapor faster and higher intensity of light will increase the rate of photosynthesis.
So that water diffuses out of the leaf through the stomata more frequently.
Plants living in different habitats have adapted well to resist the extremes of these factors and so survive.
When looking at the plants in the environment around us,
We can be aware of these factors and gain a greater understanding of just how wonderful the processes they go through every minute of every day really are.
