Explain the process of gas exchange in plants
- Air diffuses from stomata into the leaf
- Air circulates between the spongy & palisade tissue cells
- CO2 diffueses down its conventration gradient, dissolving into water around cells and then into cells
- Oxygen produced during photosynthesis passes out of the cells ino air spaces & then through stomata
- Water from the xylem exits through the stomata as water vapour.
Explain the process of photosynthesis
- 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)]
- 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)
- Chloroplasts in the palisade tissue cells & spongy tissue cells in the leaves trap sunlight energy
- CO2 enters the leaf through stomata (and lenticles)
- Chloroplats convert sunlight energy, CO2, and H2O into sugar and energy
- Sucrose is sent to other parts of the plant through the phloem.
- Water exits the leaf through stomata as vapour.
- Oxygen passes out of cells, circulates, and then exits the leaf.
Describe the process of sugar transport
- 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
- Some sap leaves the phloem to nourish the surrounding tissue as the sap travels to the roots.
- As it moves downwards the pressure in the phloem decreases
Pressure in the roots is almost always lower than the leaves
What is cohesion and adhesion? How does it help during photosynthesis?
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.
What is transpiration?
Evaporation of water from leaves that creates a constant stream of water
What is turgor pressure? What does it do?
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
Why do trees take up so much water? Why is it lost as evaporation?
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.
What are the components of a leaf?
Cuticle, epidermal cells, stomata, guard cells, palisade tissue cells, spongy tissue cells, vascular tissue cells
Cuticle
- Waxy substance
- Coats cells to prevent evaporation
- Does not have chloroplats
Epidermal cells
- Protective layer that covers plant (upper and lower)
- Tightly packed
- 1 cell layer think, otherwise could not allow sunllight, CO2 in and O2 out
Stomata
- Small openings in epidermal layer (usually on underside)
- Allows gases and water vapour in/out
Guard cells
- Located beside stomata
- Regulate stomata’s size
- Change shape to close / open stomata
Why is the relationship between guard cells and the stomata important? What determines the opening of the stomata?
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)
Palisade tissue cells
- Long and narrow, packed closely together
- Located just under leaf’s surface
- Major photosynthesizing cell, contains chloroplasts, as a result makes photosynthesis efficient
Spongy tissue cells
- 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)
Vascular tissue cells
- Forms series of tubes that transport fluids throughout plant and vascular bundles (veins seen on leaves)
- Contain xylem and phloem
Describe the xylem
- Transports water and dissolved minerals
- Moves form roots to leaves
- Located in the middle of trunk
- Hollow tubes consisting of only cell walls
Describe the phloem
- 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
What makes most of a tree’s mass?
CO2 makes up 95% of a tree’s mass, as it weighs heavier than oxygen and is not released.
Why is it important the the xylem has no air bubbles?
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)
What is root pressure?
- Pressure created when water flows into the root system to equalize concentrations of solute within root
What are tropisms? Why do they occur?
Tropisms -
Movement of plant in response to stimulus (light gravity, mechanical stimuli – ie. touch),
Result when external stimulation is unequal
What is the stimulus plants need to survive?
Light, water, and carbon dioxide
Multicellular organisms:
- What are the benefits of being a multicellular organism?
- How is a multicellular organism organized?
- Ability to have a larger size
- Variety of specialized cells
- Ability to thrive in broader range of environments
Organization (smallest to largest):
- Cells
- Tissues (cells similar clustered together)
- Organs (multiple tissues arranged to form a specific function
- Systems (organs & tissues work to perform a shared, complex function)
