Plants cells & vessels

Question 1

What is the structure of the cell wall?

Answer 1

The cell wall is a rigid covering that protects the cell. Plant, fungal and algal cells all have cell walls.

Question 2

What are cell walls made of?

Answer 2

The major organic molecule in fungal cell walls is chitin. Plant and algal walls are made of cellulose.

Question 3

What is cellulose?

Answer 3

A polysaccharide made up of beta glucose units

Question 4

What is the middle lamellae?

Answer 4

It acts as an adhesive, joining adjacent cell walls together and is made of pectin

Question 5

What is the function of cell walls?

Answer 5

The cell wall provides structural support and gives shape to the cell

Question 6

What is the structure of cell vacuoles?

Answer 6

Vacuoles are surrounded by a membrane called the tonoplast and contain a weak solution of salts and sugars called cell sap

Question 7

What is the function of the cell vacuole?

Answer 7

It allows the cell to remain rigid. When the vacuole holds more water, it is pushed against the cell wall and pressure is maintained. This stops wilting.

Question 8

What is the structure of chloroplasts?

Answer 8

A small, flattened structure. It’s surrounded by a double membrane and has membranes inside called thylakoid membranes. These are stacked up in some parts of the chloroplast to form grana. Grana are linked together by lamellae.

Question 9

What is the function of chloroplasts?

Answer 9

Photosynthesis is the series of reactions that use carbon dioxide, water and light energy to make glucose and oxygen. This allows plants to make their own food.

Question 10

What are amyloplasts?

Answer 10

Organelles which store starch granules. Glucose produced is stored as starch and can be broken down again when it is needed.

Question 11

What is plasmodesmata?

Answer 11

Small channels which allow the exchange of substances between plant cells. The channel forms in the cell walls.

Question 12

What are pits?

Answer 12

Small cavities in the cell walls of xylem vessels, which allow water to be exchanged between them. This is essential for transporting water up the plant.

Question 13

What does the xylem do?

Answer 13

Plant vessels that are responsible for transporting water and mineral ions

Question 14

What are vessel elements in xylem?

Answer 14

The xylem vessels are long, tubes of cells that run up the stem of plants. The vessel elements in the xylem are dead.

Question 15

What are end walls in xylem?

Answer 15

The vessel elements are stacked on top one another. There are no cell walls at the ends of each vessel element. This creates a continuous tube for water to flow through.

Question 16

What is lignin in xylem?

Answer 16

The walls of the xylem are lined with a waterproof polymer called lignin. It reinforces the walls of the vessel elements to provide structural support.

Question 17

What is step one in the cohesion-tension theory?

Answer 17

1) Transpiration: Some of the water in the leaves is used in respiration. Most of the water in the leaves evaporates in a process called transpiration.

Question 18

What is step two in the cohesion-tension theory?

Answer 18

2) Tension: The loss of water from the leaves creates tension in the xylem. Tension is the formation of hydrogen bonds between water molecules and the sides of the xylem vessel elements. Water in the xylem is pulled upwards by this tension towards the leaves.

Question 19

What is step three in the cohesion-tension theory?

Answer 19

3) Cohesion: Individual water molecules also form hydrogen bonds with each other. This process is called cohesion. When water molecules are pulled up the xylem, other molecules of water are also pulled upwards due to cohesion. The combination of cohesion and tension together continuously pull water upwards to replace water that has been lost in the leaves by transpiration.

Question 20

What is step four in the cohesion-tension theory?

Answer 20

4) Diffusion in the roots: When water is pulled up the stem, the water potential at the bottom of the plant decreases. Water diffuses into the roots via osmosis down its water potential gradient.

Question 21

What does the phloem do?

Answer 21

Plant vessels that are responsible for transporting sugars

Question 22

What are sieve tube elements in phloem?

Answer 22

The vessel consists of many sieve tube elements that rub up the stem on top of one another. They are living cells and their walls are made of cellulose.

Question 23

What are companion cells in phloem?

Answer 23

Companion cells are connected to sieve tube elements via plasmodesmata. Plasmodesmata allows the cytoplasm to be shared between companion cells and sieve tube elements.

Question 24

What are sieve plates in phloem?

Answer 24

At either end of the sieve tube events are sieve plates. They have large pores that allow sap to move through the elements. Sieve plates allow sugars to be transported through the phloem.

Question 25

What is step one of translocation?

Answer 25

1) Active transport of sucrose: Sucrose is produced during photosynthesis in the leaves - the source. Sucrose is actively transported into the companion cells in the phloem. Energy is provided for active transport from mitochondria in the companion cells.

Question 26

What is step two of translocation?

Answer 26

2) Diffusion of sucrose: The loading of sucrose into the phloem causes the concentration of sucrose to increase. Sucrose diffuses from the companion cells into the sieve tube elements.

Question 27

What is step three of translocation?

Answer 27

3) Osmosis: The increase in the concentration of sucrose in the phloem causes water potential in the phloem to decrease. There is a water potential gradient between the outside of the phloem and the inside. Water diffuses into the phloem by osmosis.

Question 28

What is step four of translocation?

Answer 28

4) Unloading of sucrose: At the bottom of the phloem, sucrose concentration is low because it is being used up in the cells. The cells at the bottom of the phloem are called the sink. Sucrose diffuses out of the phloem and into the sink cells. This lowers the water potential of the sink cells.

Question 29

What is step five of translocation?

Answer 29

5) Osmosis: Water diffuses down its water potential gradient out of the phloem by osmosis. The diffusion of water into the phloem at the source and out of the phloem at the sink creates a hydrostatic pressure gradient. The hydrostatic pressure gradient allows mass flow of sucrose from source to sink.

Question 30

What is the structure of sclerenchyma cells?

Answer 30

Sclerenchyma cells walls are lignified as well as containing cellulose and hemicellulose, making the walls thicker. Mature sclerenchyma cells are dead.

Question 31

What are the two types of sclerenchyma cells?

Answer 31

There are two main types of sclerenchyma cell: fibres and sclereids. The fibres are longer, and are usually found in bundles in plants. Sclereids have very thick cell walls and are responsible for the gritty texture in fruits.

Question 32

What is the function of sclerenchyma cells?

Answer 32

Sclerenchyma supports and strengthens the plant. It is found in many plants, and in most parts of the plant. Sclerenchyma fibres tend to be associated with the vascular bundles.

Question 33

What are the positions of xylem, phloem and sclerenchyma fibres in the stem?

Answer 33

Xylem is found on the inside of the vascular bundle, followed by phloem then the sclerenchyma fibres are found on the outside

Question 34

Water as a solvent

Answer 34

Water is used to transport dissolved substances in the xylem and phloem around the plant. Water in plant cells provides an aqueous environment for reactions to take place, as well as taking part in reactions urself.

Question 35

Water in transpiration

Answer 35

When water evaporates from the leaves, more water can be taken in by roots and water moves up the plant. Transpiration occurs due to the cohesion-tension theory.

Question 36

Thermal properties of water

Answer 36

Water is able to maintain a reasonably stable temperature independent of its surroundings. This helps plants to maintain a reasonably constant internal temperature.

Question 37

Cell turgidity

Answer 37

Water keeps plant cells turgid, this is important for supporting the plant. If cells are not turgid enough, then the plant loses turgor pressure and wilts.

Question 38

Water as a reactant

Answer 38

Water is needed as a reactant in photosynthesis. Photosynthesis is vital for plants so they can produce sugars to use in respiration.

Question 39

How do plants uptake ions?

Answer 39

Active transport is used because the concentration in the roots is usually much higher than in the surrounding soil

Question 40

Why do plants need nitrates?

Answer 40

Plants absorb nitrates to synthesise amino acids (building blocks of proteins). Nitrogen is also a key component of chlorophyll - a pigment which absorbs light for photosynthesis.

Question 41

Why do plants need calcium ions?

Answer 41

Calcium ions play an important role in the proper growth of new tissues, like root and shoot tips. They are also present in cell walls, and they help to stabilise the cell wall, as well as control enzyme action.

Question 42

Why do plants need magnesium ions?

Answer 42

Magnesium is an essential component of chlorophyll. Chlorophyll absorbs light to use in photosynthesis.

Question 43

What happens when plants don’t get enough needed minerals?

Answer 43

It affects their growth

Question 44

How can the effects of mineral deficiencies on plants be investigated?

Answer 44

By growing a plant on a control solution containing all minerals and comparing this to solutions which have all minerals except the one you want to investigate.