Plant Biology Konrad Pawlikowski

Transport in the Xylem of Plants

Transpiration is the inevitable consequence of gas exchange in the leaf. Transporation is the loss of water from plants through the stomata in the leaves. Guard cells help adjust the stoma and allow them to release the water. Exchange of gases sustains photosynthesis.

Plants transport water from the roots to the leaves to replace losses from transpiration. When water evaporates new water comes through the roots. Goes through Xylem. This is because of cohesion.

The cohesive property of water and the structure of the xylem vessels allow transport under tension. Xylem is a tube made of cellulose. This provides a sturdy structure for transport of minerals and water.

The adhesive property of water and evaporation generate tension forces in the leaf cell walls. Water is pulled out of the plant into the leaf. Light and temperature turns water into the vapour state. Water exits through the stomata.

Active uptake of mineral ions in the roots causes absorption of water by osmosis. Passive transport. Water from soil flows from high to low concentration. Ions go through active transport. Protein Pumps.

Adaptations of plants in deserts and in saline soils for water conservation. Plants adapt to water loss in harsh conditions. Waxy Leaves. Firs and Pines. Succulent.

Drawing the strucutre of primary xylem vessels in sections of stems based on microscope images.

Transport in the Phloem of Plants

Plants transport organic compounds from sources to sinks. Translocation, organic compounds are carried in Phloem tube.

Incompressibility of water allows transport along hydrostatic pressure gradients. Hydrostatic pressure helps move water. Water moves from high to low concentration from xylem to phloem, through osmosis. This water movement occurs when there is different water potential.

Active transport is used to load organic compounds into phloem sieve tubes at the source. Sieve tubes are specialized cells that make up the phloem. These cells are lvining and contain mitochondria used for ATP production.

High concentrations of solutes in the phloem at the source lead to water uptake by osmosis.

Raised by hydrostatic pressure causes the contents of the phloem to flow toward sinks. The translocation theory. Movement of minerals from source to sink. Water is recycled in the end.

Structure function relationships of phloem sieve tubes.

Microscope images. Notice the sieve tubes are separated.

Growth in Plants.

Undifferentiated cells in the meristems of plants allow for indeterminate growth. Plants grow only in meristems. These tissues are made of cells that undergo cell division.

Mitosis and cell division in the shoot apex provide cells needed for the extension of the stem, and development of leaves. Small cells therefore fast cycles which mean fast growth.

Plant hormones control growth in the shoot apex. Auxin- root growth. Gibberellin- cell division, flowering, size. Cytokinin- cell division, aging of leaves. Absisic acid- Stress hormone, reduces growht during times of stress.

Plant shoots response to enviromental tropisms. Tropisms are external factors that influence plant growth. Phototropism. Gravitropism.

Auxin Major role in the growht of plants. Auxin Efflux pump. Auxin changes gene expression patterns.

Reproduction in plants.

Flowering Involves a change in gene expression in the shoot apex. mRNA moves from leaf to flower meristem. Differentiation of meristem into the flower happens due to the construction of protein.

The switch to flowering is a response to the length of light and dark periods in many plants. Long and Short day plants. Each grow in different periods. Each grow depending on the enviroment they are at. Use Phytochromes which are pigments which measure length of light.

Success in plant production depends on many factors. Polination Fertalization Seed Dispersal

Most flowering plants use mutualism in sexual reproduction. Plants need polinators such as bees or insects to carry their seeds onto another plant. Both benefit as the polinator gets nectar and plants reproduce.

Methods used to induce short-day plants to flower out of season. Since the plants are mostly used to darkness they need to be covered from light. This can be done by putting a cloth over them for 15 hours a day.

Drawing of seeds.

Drawing of animal polinated flowers.

Sources Used https://sites.google.com/a/canacad.ac.jp/sl-hl-1-biology-4- ferguson/10-botany/9-3-growth-in-plants http://www.slideshare.net/smullen57/92-transport-in-the-phloem- of-plants?next_slideshow=1 http://www.slideshare.net/smullen57/ib-biology94-plant- reproduction http://www.slideshare.net/smullen57/ib-biology-91-transport-in-the- xylem-of-plants http://jxb.oxfordjournals.org/content/59/2/187.full