Roots, Stems, and Leaves 4.8 and 4.10

Roots, Stems, and Leaves4.8 and 4.10 SBI 3C

Roots, Stems, and Leaves4.8 and 4.10 • SBI 3C

Function of roots • Absorb water and minerals from the soil • Support and anchor plant • In many plants, they are main storage tissue • Good food source for other organisms (ex. Carrots, parsnips, sweet potatoes, radishes)

Taproots vs. Fibrous roots • Two most common forms of roots are taproots and fibrous roots

Taproots vs fibrous roots

Root growth and differentiation • Apical meristems, protected by a layer of cells called the root cap, are found at the tips of roots and shoots • The zone of elongation, behind the apical meristem, is where newly divided cells increase in length • The zone of maturation is where root cells differentiate and mature

Root Adaptations • What is meant by the term “root adaptations”? • Roots of many plant species have adaptations that help plants survive in their particular environments • Ex. Small aerial roots grow above-ground and help roots to absorb nutrients from rainwater or to provide additional support by grasping onto other surfaces

Stems • The shoot is made up of stems and leaves Function of stems: • Provide support for the above-ground part of the plant • Link roots with the leaves and any reproductive structures • Also store water and food

Stems of herbaceous vs woody plants • Herbaceous plants are those which lack woody tissue, whereas woody plants are those which are wood producing

Stem growth • Stems increase in length by division of cells from apical meristems, and increase in diameter by division of cells from vascular cambium • Xylem cells accumulate over time and older phloem cells are crushed by newly produced phloem cells • Bark is composed of everything from vascular cambium outwards, including phloem cells

Wood • In woody species, new xylem develops into wood • Difference in cell size between spring and summer produces visible annual ring in wood. This can be used to determine age of a woody plant.

Stem adaptations • Stems of some plants form specialized functions to best suit their particular environment • Ex. Cacti stems are adapted to store large amounts of water. Why would this be important for a cactus?

Using roots and stems • Things we attain from stems are wood, which is used for lumber, pulp, paper, and as a source of fuel; maple syrup; foods such as carrots, yams and sugar, etc. • Things we attain from roots are flavourings for drinks like root beer and ginger ale; dyes; resins; gums; tannins, etc.

Leaves • Major function is as main site of photosynthesis • Where does their green colour come from? • From chlorophyll, a green pigment • Two main types of leaves: compound and simple • Simple have continuous, undivided blade and margin while compound leaves have a blade divided into two or more leaflets

Leaf Structure • The waxy cuticle protects the leaf • The mesophyll cells are most cells in a leaf and are rich in chloroplasts • The palisade mesophyll is a layer of mesophyll cells at right angles to leaf surface • The spongy mesophyll are loosely arranged mesophyll cells within the leaves

Stomata • Photosynthesis requires exchange of gases • This exchange is done through stoma (plural stomata) which is a small opening in the surface of a leaf controlled by a pair of guard cells • Since water loss(transpiration) occurs when stoma are open, stomata help regulate this loss. • Stoma opens when guard cells absorb water, and close when they lose water • Therefore, stomata are open when in moist conditions and closed when in dry conditions

Image of stomata

Leaf adaptations • Leaves of cacti lack a leaf blade and central leaf vein is modified to form sharp spine • Conifer leaves are in form of needles or scales to help plant survive cold, dry conditions • Shade plants possess leaves that are thinner, broader or greener than leaves of sun-loving plants

Uses of leaves • Food: tea, lettuce, onions, hay for livestock, rosemary, basil, thyme • Drugs: digoxin (heart medication), nicotine (used as insecticide) • Nonmedicinal chemicals: dyes, waxes, oils used in perfumes and cosmetics

Roots, Stems, and Leaves 4.8 and 4.10