1. Topic 9 Plant Biology

2. Introduction Plants are extremely important They produce oxygen
They remove carbon dioxide from the atmosphere.
They produce food (carbohydrates)
We will study transportation (xylem & phloem), growth, and reproduction.

3. 9.1 Xylem
Water is lost as a vapor from leaf openings called stomata, called transpiration.
This lost water must be replaced by absorption.
Leaves vary in form but generally consist of the flat blade, and a stalk called the petiole that attaches the blade to the stem.

4. Structure of a leaf

5. Leaf Structure
Outer layer for many is a waxy cuticle for protection and to prevent water loss.
Next layer is epidermis which also is for protection.
Vascular tissue, xylem brings water to the leaf while phloem carries products of photosynthesis to the plant.
Both are found in bundles called veins.

6. Under the epidermis on the top of the leaf is the palisade mesophyll where most of the chloroplasts are located.
Above the epidermis on the bottom of the leaf is the spongy mesophyll, loosely packed cells with lots of room for gas exchange.
Stomata are on the bottom of the leaf and are the site of gas exchange. Water can be lost here. Protected by guard cells which control the size of the openings.

7. Water and Mineral Movement
Water lost from leaves (transpiration) is replaced by water from the roots.
This is a constant flow which also carries minerals with it.
Transpiration helps to cool leaves and stems.
Xylem is involved in this upward movement of water as well as support of the plant.

8. Xylem Two main types of cells, tracheid and vessel elements.
Tracheids are dead cells that taper at the ends and connect to form a tube.
Vessel elements are also dead cells that have thick walls supported by lignin and ave pits to allow lateral movement.
Tracheids evolved first, vessel elements came later.
Water movement within the xylem is cohesion-tension mechanism.

9. Stomata and Guard Cells
Stomata openings are controlled by the two guard cells around them.
When full of water, high turgor pressure opens the guard cells, when low on water, low turgor pressure causes the stomata to close.
Water movement is controlled by potassium ions.
Blue light causes protein pumps to pump potassium into the guard cells, which causes water to move into the cells.

10. Abscisic Acid
Abscisic acid is a hormone that causes potassium ions to rapidly diffuse out of the guard cells, causing closure.
Produced in the roots when water levels are low.
Prevents water loss from transpiration, but there’s a problem with this. What is it???

11. Cohesion-Tension Theory
Water leaves the plant due to more water in leaf than in atmosphere. (transpiration)
Lost water is replaced by water from vessels (xylem)
Water in the vessels in maintained by cohesion and adhesion.
Tension occurs on the column of water as water leaves the leaf.
Water is pulled from the root cortex into the xylem.
Water is pulled from the soil into the roots.

12. Roots and fluid movement
Main job of roots is uptake of water and minerals inn the form of ions.
Root hairs increase surface area 3X.
Root cap protects apical meristem during growth.
Root has 3 zones: cell division zone (mitosis),elongation zone where cells grow (G1), and maturation zone where cells become functional. ( root hairs etc.)

14. Mineral ions Mineral ions get into roots 3 ways: Diffusion
Fungal hyphae (symbiotic relationship) called mycorrhiza
Active transport

15. Adaptations for water conservation
Light speeds up transpiration by warming and opening stomata.
Humidity decreases transpiration
Wind increases transpiration
Temperature increases transpiration
Soil water decrease causes transpiration decrease
Carbon dioxide increase causes transpiration to decrease.

16. Desert and salt plants
Xerophytes are adapted to arid climates by limiting transpiration loss
Small thick leaves decrease surface area
Fewer stomata
Stomata found in recessed pits
Thick waxy cuticle
Hair like cells on surface help to trap moisture
Lose leaves during the driest times

17. Succulents store water in their thick stems and leaves
Xerophytes use CAM and C4 processes
CAM plants close stomata during the day and make sugar at night.
C4 plants open during the day but can bring in carbon dioxide quicker than usual.

18. Halophytes
Grow in salt
Mangroves secrete salt through glands

19. 9.2 Transport in the phloem

20. Movement of organic molecules
Organic molecules move via the phloem.
Phloem is made of living cells.
Made from sieve tube members and their companion cells.
Sieve tube members connected to each other by plates to form sieve tubes.
The plates have pores for movement.
Companion cells connect by plasmodesmata

21. Movement of organic molecules in plants is called translocation.
Fluid is called sap and is mostly sucrose, with some amino acids, hormones and RNA

22. Pressure-Flow hypothesis
The movement of sugar into and out of the phloem causes water movement into and out of the phloem from the xylem.
This causes pressure differences and aids in movement.
Used aphids to learn about this.

25. 9.3 Growth in Plants Most plants have 3 basic types of tissue
Dermal tissue, outer covering for protection and water loss.
Ground tissue, thin walled cells that do storage, photosynthesis support, secretion.
Vascular tissue, xylem and phloem, move water, minerals and nutrients around plant and offer some support.

26. All are derived from meristematic tissue, small undifferentiated cells sort of like stem cells.
When they divide, one cell remains an undifferentiated meristem, the other differentiates to become some part of the plant.
The one that stays a meristem is called an initials, the ones that differentiate are celled derivitives.

27. Unlike animals, plants grow all during their lives, called indeterminate growth.
Determinant growth ceases after a certain period of time.
Plants do die however. Some are annuals, living only one year, some are biennials, living two years, perennials live for many years and usually die from an infection or other environmental factor.

28. Apical Meristems
Apical meristems, sometimes called primary meristems, are at the tips of roots and stems.
This area is referred to as a shoot apex.
New growth is called primary growth and is mitosis.
This causes non-woody stems and roots

29. Lateral meristems Causes growth in width or thickness of plants.
Most trees and shrubs have two kinds of lateral meristems:
Vascular cambium, which is between the xylem and phloem. Makes secondary xylem that forms wood, and secondary phloem
Cork cambium, in the bark of the plant, forms outer bark.

30. Plant Hormones Factors that affect plant development:
Environmental such as day length and water availability
Receptors which allow plant to detect environmental factors.
Genetic makeup of the plant
Hormones , chemical messengers

31. Receptors in certain cells receive stimuli causing the cell to release a hormone.
Hormones have a particular cell they effect called the target cell.
Unlike animal hormones, a plant hormone can have a different effect on cells in different parts of a plant.
In animals there is usually one gland that makes a specific hormone, in plants, hormones are made throughout the plant.

32. Auxins and phototropism
Tropisms are movements based of an external stimulus.
Positive tropism is toward the stimulus, negative tropism away from the stimuli.
Common stimuli for plants are chemicals, gravity, touch, and light.
If the stimulus is light, its called phototropism.

33. Plant stems show positive phototropism while plant roots show negative.
Allows plants to move toward the light for survival.
Auxins are hormones that cause positive phototropism.
Found in the embryo of seeds, apical meristems, and young leaves.

34. Auxin only works on cells that have auxin receptors.
Auxin causes elongation of cells by making their cell walls more flexible.
Auxin is produced by all cells in the area but is goes to the side of the plant that is away from the light.
Active transport pumps auxin out of cells on the light side. Indoleacetic acid

35. Auxins interact with the nucleus of the cell changing gene expression, which activatse a proton pump that pumps protons into the cell wall and changes the pH.
This causes hydrogen bonding within the cellulose to break down.
Auxins also help with cell division, differentiation between xylem and phloem, lateral roots, growth of flowers.

36. 9.4 Reproduction in plants