Topic 13

Plant Science

13.1

Plant Structure

Plant DiversityThe plant kingdom contains widespread diversity, as shown by fundamental structural differences between four plant classifications: bryophytes, filicinophyst, coniferophytes, and angiospermophytes.

Bryophytes-Land plants that lack many standard terrestrial adaptations.Filicinophytes-Huh????Coniferophytes- Plants whose reproductive structure is the cone.Angiospermophytes-Flowering plants.

External Plant Parts

Tissue Distribution in the Stem

Tissue Distribution in the Root

Tissue Distribution in the Leaf

Distribution/Function RelationshipPalisade Parenchyma is a layer of tissue that houses cells for photosynthesis. It is at the top of the leaf, closest to the light.Spongy Mesophyll is the airy space in the middle that allows for the circulation of gases.The Xylem and Phloem are well protected for the the transport of water and sugars.The epidermis is the outside skin that protects the plant’s vital organs and maintains support.

Xerophyte AdaptationsXerophytes are plants that have adapted to dry climates, like deserts.They have small thick leaves for reduced surface area.The stomata are located in pores that offer shelter from dry wind.Some have adapted to store water in their fleshy stems.Some take in CO2 at night and close their stomata during the dry day.

Hydrophyte AdaptationsHydrophytes are plants that live in water.They have little or no structural support, because the buoyancy of the water holds them up.Many have highly divided leaves to lessen resistance to flowing water.

13.2

Transport in Angiospermophytes

Root System Surface AreaRoot systems make use of extensive branching and root hairs to increase the surface area that is able to absorb water and mineral ions through the ground.

Mineral Ion UptakeRoot hairs are permeable to water.Soil particles are usually coated with water and thus adhere tightly to the root hairs.Vital minerals are pulled from the soil solution through active transport by cells with selective membranes.A ring of waxy material blocks the parts of the solution that weren’t absorbed from entering the Xylem vessels.

Root Water AbsorbtionThere are two routes from the root hairs to the Xylem: the symplastic route is through the interior of cells, passing across permeable membranes; the apoplastic route is between the cell walls.

Water initially absorbed by the hydrophilic root hairs travels the apoplastic route. Water and vital minerals are absorbed through membranes to the symplastic route.Anything still in the apoplastic route is blocked by the Casparian strip from entering the Xylem.

Terrestrial Plant SupportThickened cellulose, cell turgor, and xylem all help to support land plants.

TranspirationTranspiration is the loss of water vapor from the leaves and stems of plants.

Transpiration StreamIn the center of the leaf, mesophyll cells are coated with a thin film of water. As water vapor diffuses through the stomata to the dry air outside, there is a force on the water film that attracts it to the hydrophillic cell walls.Cohesive forces resist a change in the surface area of the water.

A meniscus forms, which becomes tighter as transpiration increases.This meniscus causes negative pressure, which exerts a transpirational pull.This pulls the sap at the top of the xylem column, and the rest of it, down to the roots, is pulled along because of the sap cohesion.

StomataThe tiny pores on the surface of leaves, called stomata, are each surrounded by a pair of guard cells.The guard cells can open and close the stomata to regulate transpiration.

Rate of TranspirationTranspiration is the evaporation of water, so its rate is directly proportional to the intensity of sunlight and temperature.Dry air also causes a large increase in transpiration, as does wind.

PhloemPhloem sap is a multidirectional flow of sugars and other vital nutrients

Plant Food Storage

13.3

Reproduction in Flowering Plants

Flower Structure

PollinationThe placement of pollen into the stigma of a carpel by wind or animal carries.Prerequisite to fertilization.

ReproductionPollination is the process of carrying pollen from one plant to another, which can bring about fertilization.Fertilization is the union of two haploid gametes.Seed dispersal is the spreading around of fertilized embryos together with some food and vital nutrients.

Internal and External Seed Structure

GerminationAfter a seed has landed in a moist patch of soil and the absorption of water has occurred, a hormone called gibberellins in released by the embryo.This hormone triggers the starchy protective covering of the seed to begin producing amylase.

The amylase catalyses the breakdown of the protective covering from starch to maltose.The maltose produced in this reaction is taken in by the growing embryo, which is able to break out of the seed covering as it breaks down and the embryo grows.

Necessary Germination ConditionsThe most important condition for germination is the presence of water.Some desert seeds will remain in dormancy until after a strong rain, so that they are able to develop. Many seeds also require sunlight to trigger germination.