Chapter 7: Transport In Plants Flashcards
How do plants transport carbon dioxide and oxygen?
The gases diffuse through air spaces within stems, roots and leaves.
What are the two transport systems in a plant?
Xylem and phloem
What does xylem carry and where? How ref. direction?
Xylem carries mainly water and inorganic ions(mineral salts) from the roots to the parts above ground. The movement in the xylem is in one direction.
What does the phloem carry and where? Direction?
The phloem carries the substances made by photosynthesis from the leaves to other areas of the plant. At any one time, phloem sap can be moving in different directions in different parts of the phloem.
How are monocots and dicots different and similar in terms of transport?
The mechanisms of transport through both types of plant are the same, but there are differences in the distribution of xylem and phloem in their roots, stems and leaves.
What are tissues?
They are collections of cells specialised for a particular function.
What is the epidermis and what is its function?
It is the continuous layer on the outside of the plant, one cell thick, that provides protection. In leaves, it has pores called stomata.
What are some of the functions of a waxy cuticle?
It is waterproof and helps to protect the organ from drying out and from infection.
What special features does the epidermis have in these parts of the plants and what are their functions?
- stem and leaves
- leaves
- roots
- In stems and leaves, the epidermis is covered with a waxy cuticle which is waterproof and helps to protect the organ from drying out and from infection.
- In leaves, it also has pores called stomata which allow entry of carbon dioxide for photosynthesis.
- In roots, they may have extensions called root hairs to increase the surface area for absorption of water and mineral salts.
What is parenchyma and where is it found?
Parenchyma is made up of thin walled cells. It forms the cortex of stems and roots, and the pith(central region) in stems. The parenchyma in leaves contain chloroplasts, where it is modified to form the palisade and spongy mesophyll layer.
What are some of the functions of parenchyma? (6)
- They are used as packing tissue.
- They may be used for storage of food like starch.
- When they are turgid(inflated with water), they help to support the plant, preventing wilting.
- The air spaces between the cells allow gas exchange.
- Water is transported through the walls and through the protoplasts of cells.
- They can be specialised to form the palisade and spongy mesophyll layer.
What is collenchyma and what is its function? Where is it found?
Collenchyma is a modified form of parenchyma with extra cellulose deposited at the corners of cells. This provides extra strength. The midrib of leaves contain collenchyma.
Where is the endodermis found?
The endodermis is a one cell thick layer that surrounds the vascular tissue in stems and roots.
What are the two types of mesophyll? What are the differences?
Spongy mesophyll is so called because in three dimensions it is spongy in appearance because it has many large air spaces between the cells.
Palisade mesophyll cells are near the upper surface of the leaf where they receive more sunlight. They are column shaped and contain more chloroplasts than spongy mesophyll cells.
What is the pericycle? Where is it found? Describe this layer with reference to roots and stems.
This is a layer of cells, one to several cells thick, just inside the endodermis and next to the vascular tissue.
In roots, it is one cell thick and new roots can form from this layer.
In stems, it is formed from a tissue called sclerenchyma. This has dead lignified cells for extra strength.
What are the tubes of the xylem called?
Vessels
What are xylem vessels made of?
They are made from dead lignified cells known as xylem vessel elements.
What are some functions of xylem?
Xylem allows the long distance transport of water and minerals salts. It also provides mechanical support and strength.
What are the tubes of the phloem called?
Sieve tubes
What are the sieve tubes made of?
They are made from living cells called sieve tube elements
What is a function of the phloem?
It allows for the long distance transport of organic compounds, particularly the sugar sucrose.
Give a brief overview of transpiration.
The energy of the Sun causes water the evaporate from the leaves, a process called transpiration. This reduces the water potential in the leaves and sets up a water potential gradient throughout the plant. Water moves down this gradient from the soil into the plant, and then across the root into the xylem tissue in the centre. Once inside the xylem vessels, the water moves upwards through the roots to the stem and from there into the leaves.
What is transpiration? Proper
Transpiration is the loss of water vapour from a plant to its environment, by diffusion down a water potential gradient. Most transpiration takes place through the stomata in the leaves.
Describe the leaf to atmosphere part of transpiration.
The cells in the mesophyll layer are not tightly packed and have many spaces between them filled with air. The walls of the mesophyll cells are wet and some of this water evaporates into the intercellular air spaces, so that the air inside the leaf is usually saturated with water. The air in the intercellular spaces of the leaf has direct contact with the air outsides the leaf, through small pores called stomata. If there is a water potential gradient between the air outside the leaf(lower water potential) and the air inside the leaf(higher water potential), then water vapour will diffuse out of the leaf down this gradient.
Are the cells in the mesophyll layer wet?
Yes