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

Function of Leaves

1. Main photosynthetic organ2. 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 CO2 in and O2 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: O2 goes out, CO2 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 prevent drying out of leaf

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 Roots1. Anchor & support plant in ground2. Absorb water and minerals3. 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 Stems1. 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 thick-

celled & dead; transports water and dissolved minerals

– Phloem thin-celled & living; transports sugars and nutrients through stem

• Cambium layers of cells between xylem and phloem that are able to divide

Filler & protective cells xylem

phloem

cambium

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