Roots, Stems & Leaves “Principal organs of seed plants”

Roots, Stems & Leaves“Principal organs of seed plants”

Seed Plant Structure3 Tissue Types:Dermal Tissue - outer covering, epidermal cells

Vascular Tissue - xylem / phloem, transport system

Ground Tissue (between dermal / vascular)

- parenchyma, collenchyma and sclerenchyma cells

23-2 Roots – Try This:http://www.virted.org/Plants/RootsQuiz.html

• Absorbs water and dissolved nutrients

• Anchors plants to ground• Prevents erosion• Protection from soil bacteria and

fungus• Transports water & nutrients• Holds plants upright against forces

such as wind and rain

Roots – Two main types:

Plants have taproots, fibrous roots or both#1 Taproots - Characterized by having one main

root (the taproot) from which smaller branch roots emerge. 

• When a seed germinates, the first root to emerge is the radicle, or primary root.  In conifers and most dicots, this radicle develops into the taproot.  

• Taproots can be modified for use in storage (usually carbohydrates) such as those found in sugar beet or carrot or radishes or turnips …. 

• Taproots are also important adaptations for searching for water, as those long taproots found in mesquite and poison ivy.

Taproot

#2. Fibrous Roots – • Characterized by having a mass of similarly sized

roots.  • In this case the radicle from a germinating seed

is short lived and is replaced by adventitious roots. Adventitious roots are roots that form on plant organs other than roots. 

• Most monocots have fibrous root systems.  • Some fibrous roots are used as storage; for

example sweet potatoes form on fibrous roots.  • Plants with fibrous roots systems are excellent

for erosion control, because the mass of roots cling to soil particles.

Fibrous Roots - A cabbage seedling with

white, fibrous roots snaking through the soil

Root Overview

(new cells produced here) (undifferentiated)

Meristematic tissue

- only plant tissue that produces new cells by

mitosis

Root Cap

- protects the meristematic tissue, thick cells to push through soil

Apical meristem

- near the tip of roots and stems

- cells increase the length of roots and stems

- undifferentiated

Zone of elongation

- where new cells are enlarging

23-3 Stems

Stems have 3 important functions:

1. Produce leaves, branches, flowers

2. Hold leaves up to sunlight

3. Transport substances between roots and leaves

23-4 Leaves

• The leaves of a plant are its main organs of photosynthesis.(plant leaves are the world’s most important manufacturers of food)

• The structure of a leaf is optimized for absorbing light and carrying out photosynthesis.

More about leaves…

• The vascular tissues of leaves are connected directly to the vascular of stems, making them part of the plant’s transport system. The vascular bundle (xylem and phloem) appear as “veins” in the leaves.

Leaf cross-section

Leaf Cross section cont…

• Cuticle – (together with epidermal cells) form a waterproof barrier that protects tissue and limits water loss.

• Epidermis – the top and bottom layer of leaves made of tough, irregularly shaped cells.

• Mesophyll – (palisade/spongy) bulk of most leaves. Where photosynthesis occurs. Sugars are produced and move into the phloem vessels to be carried to the rest of plant

Palisade – rich in plastids (chloro/chromoplasts)Spongy – rich in plastids/spaces for gas exchange

Leaf cross-section cont…

• Stomata (stoma) – porelike openings in the underside of the leaf that allow CO2 and O2 to diffuse in and out of the leaf.

• Guard cells – each stoma consist of 2 of these that control the opening and closing of stomata by responding to changes in water pressure.

Leaves• Photosynthetic organ of the plant,

used to convert sunlight into food • Photosynthesis Equation:

Notes:

• cuticle - top / bottom (thicker on top most of the time)• epidermis - top/bottom• air spaces in spongy mesophyll

• stoma surrounded by guard cells• generally more stoma on the bottom than on the top (stomata is both

stoma and guard cells)

• when the plant has lots of water, the guard cells are full and they move apart opening the stoma; when the plant is lacking in water, the guard cells close

• finally, stoma are open in the day; its needed for photosynthesis

• Most plants, stoma are closed at night when plant doesn't need CO2 (go to link)

• plants gain CO2 while losing water

• http://www.ftexploring.com/photosyn/chloroplast.html