Bio - Plants

Question 1

Explain the process of gas exchange in plants

Answer 1

1. Air diffuses from stomata into the leaf
2. Air circulates between the spongy & palisade tissue cells
3. CO₂ diffueses down its conventration gradient, dissolving into water around cells and then into cells
4. Oxygen produced during photosynthesis passes out of the cells ino air spaces & then through stomata
5. Water from the xylem exits through the stomata as water vapour.

Question 2

Explain the process of photosynthesis

Answer 2

1. Water and minerals in the soil are attracted by the roots’ high surface area to volume ratio. [ Minerals are transported through active transport. Water enters the leaf through osmosis to dilute the amount of solute (minerals in the root)]
2. Root pressure pulls water up 1 metre then the pull of transpiration pulls the water up the xylem (with the help of cohesion and adhesion)
3. Chloroplasts in the palisade tissue cells & spongy tissue cells in the leaves trap sunlight energy
4. CO₂ enters the leaf through stomata (and lenticles)
5. Chloroplats convert sunlight energy, CO₂, and H₂O into sugar and energy
6. Sucrose is sent to other parts of the plant through the phloem.
7. Water exits the leaf through stomata as vapour.
8. Oxygen passes out of cells, circulates, and then exits the leaf.

Question 3

Describe the process of sugar transport

Answer 3

1. Sucrose enters the phloem in the leaf, creating a high concentration. Water diffuses into the phloem to dilute the solution, leading to an increase in pressure in the phloem
2. Some sap leaves the phloem to nourish the surrounding tissue as the sap travels to the roots.
3. As it moves downwards the pressure in the phloem decreases

Pressure in the roots is almost always lower than the leaves

Question 4

What is cohesion and adhesion? How does it help during photosynthesis?

Answer 4

Cohesion - H₂O molecules stick together

Adhesion - H₂O molecules stick to other substances

These characteristics assist during photosynthesis as they work alongside transpiration to draw water upwards when turgor pressure from the roots isn’t enough.

Question 5

What is transpiration?

Answer 5

Evaporation of water from leaves that creates a constant stream of water

Question 6

What is turgor pressure? What does it do?

Answer 6

Acts as a plant’s “skeleton”

• Cells with high turgor pressure have firm, rigid shapes
• Non-woody plants need high turgor pressure to stay upright

Question 7

Why do trees take up so much water? Why is it lost as evaporation?

Answer 7

Up to 99% of water absorbed by the tree is then lost through evaporation in order for the tree to gain CO₂.

For each molecule of CO₂, it loses hundreds of H₂O molecules.

Question 8

What are the components of a leaf?

Answer 8

Cuticle, epidermal cells, stomata, guard cells, palisade tissue cells, spongy tissue cells, vascular tissue cells

Question 9

Cuticle

Answer 9

• Waxy substance
• Coats cells to prevent evaporation
• Does not have chloroplats

Question 10

Epidermal cells

Answer 10

• Protective layer that covers plant (upper and lower)
• Tightly packed
• 1 cell layer think, otherwise could not allow sunllight, CO₂ in and O₂ out

Question 11

Stomata

Answer 11

• Small openings in epidermal layer (usually on underside)
• Allows gases and water vapour in/out

Question 12

Guard cells

Answer 12

• Located beside stomata
• Regulate stomata’s size
• Change shape to close / open stomata

Question 13

Why is the relationship between guard cells and the stomata important? What determines the opening of the stomata?

Answer 13

Gaurd cells change their shape to allow stomata to open/close

• When open, more photosynthesis occurs
• When closed, less photosynthesis occurs

The opening of the stomata is dependent on how much water is in the guard cells

• Hypotonic (increase in water pressure)- open from turgor pressure to let water in out
• Isotonic - Open/close
• Hypertonic - closed to conserve water (keep it in)

Question 14

Palisade tissue cells

Answer 14

• Long and narrow, packed closely together
• Located just under leaf’s surface
• Major photosynthesizing cell, contains chloroplasts, as a result makes photosynthesis efficient

Question 15

Spongy tissue cells

Answer 15

• Round and loosely packed with many air spaces (like a sponge)
• Contain chloroplasts, carry out photosynthesis
• Help out with gas and water exchange with environment (helps release oxgen)

Question 16

Vascular tissue cells

Answer 16

• Forms series of tubes that transport fluids throughout plant and vascular bundles (veins seen on leaves)
• Contain xylem and phloem

Question 17

Describe the xylem

Answer 17

• Transports water and dissolved minerals
• Moves form roots to leaves
• Located in the middle of trunk
• Hollow tubes consisting of only cell walls

Question 18

Describe the phloem

Answer 18

• Trasnports sugars created by photosynthesis
• Moves from the leaves to the rest of the plant
• Forms ring around xylem, located under bark
• Living cells, have porous cell walls to exchange materials with surrounding cells

Question 19

What makes most of a tree’s mass?

Answer 19

CO2 makes up 95% of a tree’s mass, as it weighs heavier than oxygen and is not released.

Question 20

Why is it important the the xylem has no air bubbles?

Answer 20

Air bubbles break the chain of intermolecular bonds between the water molecules, essentially shutting off flow of water. (Water is a vital element in photosynthesis)

Question 21

What is root pressure?

Answer 21

• Pressure created when water flows into the root system to equalize concentrations of solute within root

Question 22

What are tropisms? Why do they occur?

Answer 22

Tropisms -

Movement of plant in response to stimulus (light gravity, mechanical stimuli – ie. touch),

Result when external stimulation is unequal

Question 23

What is the stimulus plants need to survive?

Answer 23

Light, water, and carbon dioxide

Question 24

Multicellular organisms:

• What are the benefits of being a multicellular organism?
• How is a multicellular organism organized?

Answer 24

• Ability to have a larger size
• Variety of specialized cells
• Ability to thrive in broader range of environments

Organization (smallest to largest):

1. Cells
2. Tissues (cells similar clustered together)
3. Organs (multiple tissues arranged to form a specific function
4. Systems (organs & tissues work to perform a shared, complex function)

Question 25

Explain phototropism

Answer 25

Growth of plants toward light

• Maximies amount of light absorbed by the plant’s leaves, increases absorption of light
• Makes more photosynthesis possible, which fuels further plant growth
• Cells farther from light grow elongated

Positive phototropism - growth towards light [ie. leaves, stems]

Negative phototropism - growth away from light [ie. roots]

Question 26

Describe the investigations of phototropism

Answer 26

• Darwin* - studied which part of plant responds to light stimulus (plant tips)
• Boysen–Jensen* - tried to determine how plant tips were communicating with the area of elongation, thought growth response was result of chemical
• F. W. Went* - isolated auxin (plant growth hormone)

Question 27

Explain gravitropism

Answer 27

Growth in response to Earth’s gravitational force

Positive gravitropism - grow towards gravity [ie. roots]

Negative gravitropism - grow away from gravity [ie. stems]