Parts of a Plant Leaves Roots Stems and

Parts of a Plant – Leaves, Roots, Stems and Tissues

Function of Leaves 1. Main photosynthetic organ 2. Broad, flat surface increases surface area for light absorption 3. Have systems to prevent water loss • • Stomata open in day but close at night or when hot to conserve water Waxy cuticle on surface 4. System of gas exchange • Allow CO 2 in and O 2 out of leaf Elephant Ear Plant

Leaf Structure: Overview • Epidermis is a waxy cuticle layer to prevent water loss • Mesophyll (palisade and spongy) takes up most of the leaf layer – Most of chlorophyll for photosynthesis is found here • Moist air spaces allow for gas exchange • Vein carry water, nutrients and gases

Leaf Structure: Stoma and Guard Cells • Stoma is a small opening (pore) in the leaf – Open: O 2 goes out, CO 2 comes in (or water comes in/out) – Closed: No gas exchange (or water stays inside the leaf) • Guard cells – pair controls the opening and closing of stoma • Stoma will be open when climate is moist (water is available). When climate is dry and water is scarce, stoma will close as to Pea leaf stomata

• Leaf Adaptations Cacti live in dry climates. Leaves would be futile (water loss = death of plant). It has been modified into a spine to prevent water loss • Conifers have thin, short waxy needles instead of leaves. Windy, cold and dry climates would kill the plant. The needles keeps the water in. • Shade plants have more chlorophyll, are thicker, wider and greener. It helps them photosynthesize in low light • Sun-loving plants photosynthesize in high light, so thinner leaves help them with this.

Photosynthesis • Process by which plants convert carbon dioxide, sunlight and water to oxygen, sugar and energy – Occurs in chloroplasts of plant cells – Chlorophyll pigment in thylakoid of chloroplast absorbs the light energy to start process

Function of Roots 1. Anchor & support plant in ground 2. Absorb water and minerals 3. Hold soil in place Taproots have large main root with shorter branches. Fibrous roots is a network of similarly sized smaller roots (no main root) Roots do have adaptations. Some of which are: • Grow above-ground to collect more water • Aerial plants can grow downwards on top of standing plants, killing them. This allows the aerial plant to obtain the food, water and light they need for survival.

Root Growth 1. Root Hairs (collect water and nutrients) 2. Zone of Maturation (where root cells become mature) 3. Zone of Elongation (lengthening of root cells) 4. Zone of Cell Division (includes Apical Meristem, which generates new cells) 5. Root cap (protective cap)

Function of Stems 1. Support system for plant body – Woody plant stems are hard to bend whereas most flowering plants are softer 2. Transport system carries water & nutrients (through vascular tissue!) 3. Holds leaves & branches upright Stem Growth of Woody Plant: Looking at the picture below: What years had the most rain? What years experienced the worst drought?

Stem Adaptations and Uses Stem Adaptations • Cacti plants have large stems to hold water • Some plants have parts of them stem underground that shoot off to form new plants = reproduction Practical Uses: • Woody plants for wood, paper, fuel, etc • Maple syrup, root beer, ginger & ginger ale, gum (from Chicle tree) • Dyes, resins, gums and tannins

Vascular Tissues • Instead of arteries, veins and capillaries, plants have two types of vascular tissue in stems: – Xylem thickcelled & dead; transports water and dissolved minerals – Phloem thincelled & living; transports sugars and nutrients through stem • Cambium layers of cells between xylem and phloem Filler & protective cells that are able to divide phloem cambium xylem

Vascular Cambium • Vascular cambium forms a continuous cylindrical layer inside the stem that can reproduce • Vascular cambium cells divide to form new xylem cells towards the inside of the stem and new phloem toward the outside of the stem • Form tree rings (wood consists entirely of xylem) • Heartwood: Supports the tree (no transport) • Sapwood: Conducts water and nutrients • Cork: protects the tree • Phloem: transports sugar and nutrients