1. Plants
What is a Plant?

2. Plant Biology Basic Leaf Structure
Water is lost in the form of a gas through openings called stomata (singular stoma)
Transpiration – The term given to the loss of water vapor from leaves and other aerial parts of the plant

3. Plant Biology Transpiration can be affected by: Temperature Humidity
Wind Speed

4. Plant Biology

5. Plant Biology
Transpired water has to be replaced by the intake of water at the roots
There is a continuous stream of water from the roots to the upper part of the plant
The stream of water provides the plants with minerals and water needed for photosynthesis
Epidermis of most plants secrete wax to form a water proof coating to the leaf (waxy cuticle)

6. Plant Biology
Xylem
Involved in supporting the plant as well as being the specialized water-conducting tissue of terrestrial plants

7. Plant Biology
Xylem
A tissue that carries water upward from the roots to every part of the plant
Xylem is actually a complex tissue composed of many cell types.
The 2 types of cells largely involved in water transport are tracheids and vessel elements.

8. Plant Biology
Xylem
Tracheids are dead cells that taper at the ends and connect to one another to form a continuous column
specialized type of water conducting cell
Vessel elements are the most important xylem cells involved in water transport
Also dead cells
Have thick lignified secondary walls
Lignified walls are interrupted by areas called primary
walls

9. Plant Biology
Xylem
Primary walls include pits and pores that allow water to move laterally
Lignin - cellulose that thickens the walls of xylem to prevent inward collapse in times of low pressure.
Thickening cell walls with lignin make walls hard and “woody”
See page 384

10. Plant Biology
Must be able to draw

11. Stomata and Guard Cells
Plant Biology
Stomata and Guard Cells
Plants take in carbon dioxide (CO₂) and give off oxygen (O₂)
Stomata – openings of the leaves that allow for
gas exchange

12. Plant Biology
Plants maintain homeostasis by keeping their stomata open just enough to allow photosynthesis to take place but not so much that the lose an excess amount of water
Guard Cells – highly specialized cells that surround
the stomata and control their
openings and closing
The stomata open and close because of changes in the turgor pressure of the guard cells that surround them
When the cells take in water they swell, they bulge more to the outside – open stomata

13. Plant Biology Guard Cells opposite occurs when H₂O is scarce
When the guard cells lose water they sag towards each other – close the stomata

14. Plant Biology Guard Cells Regulate the movement of gases
Especially water vapor and CO₂ in and out of the leaf
When H₂O is abundant, it raises the H₂O pressure and opens the stomata
CO₂ can enter the through the stoma and H₂O is lost by transpiration
The gain or loss of water in the guard cells is largely because of the transport of potassium ions.

15. Plant Biology
Generally; stomata are open during the daytime (active photosynthesis) and closed at night
Can close also during bright sunlight
Guard cells also respond to wind and temperature

16. Plant Biology-Cohesion-Tension Theory
Process
Explanation
Water moves down concentration gradients
The spaces within a leaf have a high concentration of water vapor. Water moves from this location to the atmosphere, which has a lower water concentration
Water lost by transpiration is replaced by water from the vessels
Replacing water from the vessels maintains a high water vapor concentration in the air spaces of the leaf
The vessel water column is maintained by cohesion and adhesion
Cohesion involves the hydrogen bonds that form between water molecules. Adhesion involves the hydrogen bonds that form between water molecules and the sides of the vessels; adhesion counteracts gravity

17. Plant Biology-Cohesion-Tension Theory
Process
Explanation
Tension occurs in the columns of water in the xylem
This is because of the loss of water in the leaves and the replacement of that lost water by xylem water. The water columns remain continuous because of cohesion and adhesion
Water is pulled from the root cortex into xylem cells
Cohesion and adhesion maintain the columns under the tension created by transpiration
Water is pulled from the soil into the roots
This happens because of the tension created by transpiration and the maintenance of a continuous column of water

19. Plant Biology Water and Osmosis
Water is a raw material for photosynthesis
As water is absorbed minerals (nutrients) are absorbed from the soil needed for plant growth
Water moves into the root hairs from the soil because the root hairs have a higher solute concentration and a lower water concentration from the surrounding soil
Water moves through the plasma membrane into the root hair cells
Most of the water entering a plant comes in through the root hairs by osmosis

20. Plant Biology Phloem – transports solutions of nutrients and
carbohydrates (organic material)
Made up of living cells (xylem are not)
Xylem moves water and minerals upward from the roots
Phloem cells transport their contents in various direction

21. Plant Biology

22. Plant Biology
Sink – a plant organ that uses or stores sugar

23. How cells pull water upward…
Cohesion – a property of water; water molecules
are attached to one another
Cohesion is formed by Hydrogen bonds

24. How cells pull water upward…
Adhesion – water’s hydrogen bonds, bond to other
substances or attraction between
unlike molecules
Capillary Action – the tendency of water to rise in a
thin tube
It is a combination of both cohesion and adhesion
Both are also properties of water

25. How cells pull water upward…
Capillary Action
adhesion

26. Plant Biology Pressure – Flow Hypothesis
Remember that in the phloem sieve tube cells are alive
Active transport moves sugar into the sieve tube from surrounding tissues
The uptake of water at the source causes a positive pressure called hydrostatic pressure, in the sieve tube
This results in bulk flow of the phloem sap
Water then follows by osmosis, creating pressure in the tube at the source of the sugars
Hydrostatic pressure is controlled by the removal of sugar from the sieve tube at the sink
Sugars are turned to starch at the sink (starch in insoluble to water)
If another region of the plant needs sugars they are actively pumped out of the tube into surrounding tissues

27. Plant Biology
Osmosis causes water to leave the tube reducing the pressure in the tube in these areas
Results: pressure driven flow of nutrient rich sap from the sources of sugars to the places where sugars are stored or used
Xylem recycles relatively pure water by carrying it back to the source

28. Plant Biology Growth in Plants
Meristematic tissue is composed of aggregates of small cells that have the same function as stem cells in animals.
When these cells divide, one cell remains meristematic while other is free to differentiate and become part of the plant body.

29. Plant Biology Growth in Plants
Apical Meristems – AKA Primary Meristems, occur at the tips and stems
Shoot Apex – a typical meristems and the surrounding developing tissue
Primary growth allows the root to extend throughout the soil
Also allows the stem to grow to collect CO2 and light

30. Plant Biology Lateral Meristems – allow growth in thickness of plants
Secondary growth
Trees (woody plants) have active lateral meristems

31. Plant Biology Auxins & Phototropism
Tropisms – growth or movement to directional external stimuli such as light, gravity, chemical, and touch
Positive – towards stimuli
Negative – away from stimuli
Phototropism – the tendency of a plant to grow towards a light source
Plants usually exhibit a positive phototropism and plant roots exhibit a negative phototropism

32. Plant Biology
Auxins & Phototropism
Auxins are plant hormones that cause the positive phototropism of plant shoots and seedlings
Found in: embryo of seeds, the meristems of apical buds and young leaves
Auxins appear to increase the flexibility of plant cell walls in young developing shoots.
This enables cell elongation on the side of the shoot necessary to cause growth towards the light

33. Plant Biology
Auxins & Phototropism
Auxin Efflux Pumps – specialized membrane proteins, move auxin out of the cells closer to the light using ATP
This pumping action creates a high concentration of auxin in the intercellular space
The result is high concentration gradient from the intercellular space from the adjacent cell
The result is a greater elongation of cells on the stem side away from the light and then curvature towards the light

34. Plant Biology
Whenever auxin affects cell growth it does so by changing the pattern of gene expression

35. Plant Biology Angiosperms Flowering plants
Bear their seeds in flowers inside a layer of tissue that protects the seed.
Flowering involves a change in gene expression in the shoot apex
The switch to flowering is a response to the length of light and dark periods in many plants

36. Plant Biology Flowers and Fruits
Ovaries – contained in flower, they surround and
protect the seeds
Thus the name Angiosperm which means “enclosed seed”

37. Reproduction in Flowering Plants

38. Plant Biology Flower Part Function Sepals Petals
Protect the developing flower while it is inside the bud
Petals
Often colorful to attract pollinators
Anther
Part of the stamen that produces the male sex cells (pollen)
Filament
Stalk of the stamen that holds up the anther
Stigma
Sticky top of the carpel, on which pollen lands
Style
Structure of the carpel that supports the stigma
Ovary
Base of the carpel in which the female sex cells develop

39. Plant Biology Pollination – the transfer of pollen from the
male reproductive structure to the
female reproductive structure
Success in plant reproduction depends on pollination fertilization, and seed dispersal
Most flowering plants use mutualistic relationships with pollinators in sexual reproduction

40. Plant Biology
Seed – a plant embryo and a food supply, encased in a protective covering
Seed Coat
Cotyledons
Shoot Apex (embryonic shoot)
Micropyle
Hilum
Root Apex (embryonic root)

41. Factors Needed for Seed Germination
Plant Biology
Factors Needed for Seed Germination
Water must be available
Oxygen
Warmth (enzyme activity)