Topic 9 - Plant science Flashcards
Draw a diagram to show the distribution of tissues in the leaf of a plant
Draw a diagram to show the distribution of tissues in the stem of a plant
Outline the differences between the structures of dicotyledonous and monocotyledonous plants
How does the distribution of tissues help the function of the leaf in dicotyledonous plants?
- The waxy cuticle prevents loss of water and insect invasion
- The vascular bundles are located in the middle of the leaf to provide easy access to everywhere in the leaf
- Palisade mesophyll on the upper side consists of densely packed chloroplasts to ensure efficient photosynthesis (this side is exposed to sunlight)
- Spongy mesophyll on the lower side have loosely packed cells with few chloroplasts and lots of air spaces for efficient gas exchange
- Stomata on the bottom surface allow oxygen and carbon dioxide exchange from the bottom side (less water lost)
- Guard cells around the stomata control the opening and closing of them
Describe storage roots
- Specialised cells within the root store large quantities of carbohydrates and water
e. g. carrots and beets
Describe bulbs
- Vertical, underground stems consisting of enlarged bases of leaves that store food
e. g. onions
Describe stem tubers
- Horizontally growing stems below ground that are modified as carbohydrate-storage structures
e. g. potatoes
Describe tendrils
- Modified leaf structures that coil around objects to aid in support and climbing (may also be formed from modified stems)
e. g. pea plants
What kind of meristems do dicotyledonous plants have?
Apical and lateral
What is meristem?
Undifferentiated tissue that can initiate further growth
What are apical meristems?
- Tissue that occurs at the tips of roots and stems of plants
- Produces primary tissues and causes primary growth
- Allows the root to extend to the soil and also allows the stem to grow longer
- Increases exposure to light and carbon dioxide
- Results in herbaceous, non-woody stems and roots
What are lateral meristems?
- Allow growth in thickness of plants
- Secondary growth
- Most treems and shrubs have active lateral meristems
Two types:
- Vascular cambium produces secondary vascular tissue → on the inside it produces secondary xylem and on the outside produces secondary phloem
- Cork cambium occurs within the bark of a plant and produces the cork cells of the outer bark
What is auxin?
A plant hormone that causes positive phototropism of plant shoots and seedlings
How does auxin control plant growth and create phototropism?
When exposed to light, auxin becomes redistributed to the stem side away from the light source and excess growth on that side of the plant. This causes the plant to curve towards the light source, thus receive more light.
How does the root system provide a large surface area for mineral ion and water uptake?
They branch and grow root hairs which further increase the total surface area.
In what ways can mineral ions in the soil move to the root?
- Diffusion
- Aid provided by fungal hyphae (mutualism)
- Mass flow of water in the soil carrying ions
Explain the process of mineral ion absorption from the soil into roots by active transport
- Proton pump uses energy from ATP to pump hydrogen ions out of the cell
- A concentration gradient of hydrogen ions is created outside the cell → cell has a negative charge
- Gradien results in the diffusion of hydrogen ions back into the cell
- The voltage difference is called a membrane potential
- The hydrogen ion gradient and the membrane potential represent forms of potential energy that can be used to absorb mineral ions
How do terrestial plants support themselves?
- Thickened cellulose → cell wall is stronger
- Cell turgor pressure → pressure exerted on the cell wall by the plasma membrane, due to water inside the cell
- Lignified xylem → branched polymer, lignified cells have much incraesed supportive capabilities
What is transpiration?
The loss of water vapour from the leaves and stems of plants.
How does water move by the transpiration stream in plants?
- Xylem vessels contain long unbroken columns of water (held together by hydrogen bonds)
- During transpiration, water moves upwards from the roots to the leaves (transpiration stream)
- Mature xylem vessels are dead, flow of water is passive
- Adhesion sticks water to the wall of xylem
1. Heat causes evaporation of water from spongy mesophyll
2. Water that evaporates is replaced with water from xylem vessels (capillary action)
3. Suction is created inside xylem vessels when water is pulled out (transpiration pull)
4. Columns of water don’t break due to cohesion
5. Basically the whole column of water moves upwards molecule by molecule, each molecule pulling another molecule from the roots ‘til exiting from the leaf
What is the function of guard cells?
They can regulate transpiration by opening and closing stomata
Which hormone causes the closing of stomata?
Abscisic acid.
How do light, temperature, wind, and humidity affect the rate of transpiration?
Light: speeds up transiration by warming the leaf and opening stomata
Temperature: increasing temperature causes greater transpiration because more water evaporates
Wind: increases the rate of transpiration because humid air near the stomata is carried away (the wind catches water molecules)
Humidity: decreasing humidity increases transpiration because of the greater difference in water concentration
What are adaptations of xerophytes that help them reduce transpiration?
- Reduced leaves reduce water loss by decreasing surface area
- Hair-like cells on the leaf surface trap a layer of water vapour
- Deep roots
- Thickened waxy cuticle
- Reduced number of stomata decreases water loss
