Plants

Based on Mader, Sylvia S. 1996. Biology - 5th Ed. WCB

and

Cox, G.W. 1997. Conservation Biology - 2nd ed. WCB

and

Levine, J.S. and K.R. Miller. 1994. Biology: Discovering Life. D.C. Heath

Reading: Chapters 30, 32 in Levine and Miller

Plants

1. Basic Needs
2. Sunlight

   Trees grow to it

   Algae may swim to it

   Need for support

3. Water
   1. Need for roots
4. Reproduction

   Special structures

   Plants can’t move

   Replacement of water as a means for mixing gametes

Evolution – movement onto land

Must solve 3 problems (5 in book)

1. Support
2. Water to leaves
   1. A lot of work to raise gallons of water to the top of a tall tree
3. Replacing water as a medium for sperm to swim in

Solutions

1. Roots
2. Vascular tissue
3. Pollen

Parts of a plant:

Three main parts:

1. Roots – obtain water, nutrients, anchor plant
2. Stems – hold up plant, transfer water, nutrients, sap
3. Leaves – photosynthetic center

3 tissues

1. dermal tissue - protection
2. vascular tissue – moving materials
3. ground tissue – support, photosynthesis

Meristems

Apical meristem

1. at the tips of roots
2. increase in length

lateral meristem

1. circles stems and roots
2. increase in girth

differentiation – transformation of one of the divided meristem cells into a specialized cell

Cell types:

1. Epidermal cells
   1. Guard cells
2. Parenchyma cells – ground tissue
3. Xylem – transports water, minerals up
   1. Comprised of tracheids or vessel elements
   2. Transport water
   3. Dead when functional

1. Phloem – transports sap – both ways

1. Sieve-tube members – no nucleus
2. Companion cells

Roots

1. Primary roots
2. Secondary roots
3. epidermis
   1. Root hairs
4. Cortex
5. Endodermis
   1. Casparian strip

Water movement

3 forces:

1. root pressure
2. capillary action
3. transpiration

   transpiration is made effective by:

   1. tension - "pull" from leaves
   2. cohesion – water molecules stick together
   3. adhesion – water sticks to walls of xylem

Ultimately powered by the sun

100 liters/day = 4 liters/hr = 4 kg/hr = 10 pounds / hr up 300 feet.

Sap movement

Pressure/flow hypothesis

1. Sugars produced in leaves
2. Sugars pumped into phloem
3. Water follows by osmosis
4. Roots remove sugar, cause gradient which draws sugar and water to roots
5. Water usually moves in the opposite direction of sap

Water uptake by roots

1. Active transport of mineral ions into roots
2. Water follows due to osmotic pressure
3. Endodermis and Casparian strip regulate water flow – water must move through cells
4. High salt levels in soil can pull water out of the root hairs

1. Halophytes tolerate higher salt concentrations

Tree stems

1. Two layers of meristem tissue
   1. Vascular cambium produces new xylem to inside, phloem to outside
   2. Cork cambium forms new cork (bark) to outside
2. Annual rings – xylem produced more rapidly in spring

Plant Growth

Seeds

Three parts

1. Embryo
2. Stored food
3. Seed coat

Monocots:

1. One cotyledon
2. Food stored in endosperm
3. Grasses (corn, rice, wheat, etc)

Dicots:

1. Two cotyledons
2. Food stored in cotyledons
3. Woody plants

Dormancy

1. Period of inactivity by the seed
2. Allows bad growing seasons to be bypassed
3. May last days to 12,000 years
4. Many seeds need drought, damage to seed coat, or freezing temperatures before germination

Plant nutrients – Table 32.2 page 643

Materials needed for photosynthesis

Water - source of hydrogen

1. taken in through roots
2. aided by mycorrhizae
3. transported up trunk via xylem
4. lost through stomata - transpiration
5. Stomata open due to turgor pressure
6. Turgor pressure requires water
7. No water - stomata close, reduces water loss

CO2 - source of carbon

1. Taken in at stomata
2. Stomata open only when water available
3. Taken in at night by desert plants

Nitrogen - needed for amino acids

1. Taken in as NO3- dissolved in H2O
2. Nitrogen fixed by bacteria in soil
3. Nitrogen present in animal wastes, fertilizers
4. Rhizobium in nodules of legumes also fix N2
5. In short supply for bog plants --> carnivory

Phosphorous - used in ATP, DNA, cell membranes

1. Taken in with water as PO4
2. uptake enhanced by mycorrhizae
3. "mined" from decaying organisms

Magnesium - used in chlorophyll

1. taken up with water

Sources of minerals

Fertilizers

1. N-P-K ratios --> nitrogen - phosphorous - potassium
2. Elements removed from soil most quickly
3. 5-10-5 NPK = 5% nitrogen, 10% phosphorous, 5% potassium
4. Test soil to determine proper ratio

Mineral availability - affected by soil

1. Property of pH - acids leach minerals from soils
2. Under acid conditions soil releases aluminum and iron rather than calcium, magnesium and potassium
3. Aluminum and iron may be toxic to the plant
4. Plants can use energy to concentrate minerals far above levels found in the soil

Epiphytes - getting by without soil

1. Some have roots, get water from atmosphere or rain
2. Bromeliads
3. Some send haustoria into plant for water or sugars or both

Agriculture

1. Human recreation of natural systems
2. Only cycles if wastes returned to soil
3. Otherwise --> mining soil

Practices:

preparing soil

1. slash-and-burn
2. machinery
3. soil erosion
4. use of fossil fuels
5. soil compaction

monoculture

1. efficiency
2. susceptibility to disease, pests

fertilizers

1. replace lost nutrients
2. expense
3. eutrophication

pesticides

1. attempt to deal with pest problems caused by monoculture

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