Unit 3 Biology

Woody Stem Key Features

What is apical bud?

Main growing bud located at the very tip of a plant stem or branch

How do plants grow and why?

Plants grow by growing longer tips and roots, because there is apical meristems (meristematic tissue), plant tissue capable of producing new cells by mitosis.

Axillary or lateral buds?

Axillary bud is the bud that will give rise to new branches 

Why do axillary buds not grow?

Meristems are also found in the axillary or lateral buds. These buds do not grow because of apical dominance where hormones produced by the apical buds inhibit side branching

Leaf scar

Leaf scar is the scar left when a leaf falls from stem

Lenticels

Lenticels are openings for gas exchange. CO2 and water vapour exit the plant and oxygen enters

The function of the stem

1. To support aerial parts of the plant

2. Transport  material

3. Photosynthesus

4. Food storage

Structure of the leaf

Features of the leaf

• Thin flat lamina

• Petiole

• Ventation

Why do leaves have a thin flat lamina?

It allows it to be well adapted for photosynthesis.

• Thin allows rapid diffusion of gases. 

• Broad and flat surface allows them to absorb maximal sunlight

Why do leaves have a ventation?

Attached to the petiole & contains vascular tissue. Smaller veins branch off it.

It can be netted or ventriculate ventilation or it can be parallel.

Why do leaves have a Petiole?

Petiole: This attaches the stem of the leaf to the stalk of the plant. It contains vascular tissue such as xylem and phloem; phloem transports food to other parts of the plant and xylem transports water into the leaf.

Functions of the leaf

Photosynthesis

To store food

Gas exchange

Transpiration (loss of water vapour from the underside of the plant

Plant Tissue:

Ground, dermal and vascular tissue

Dermal tissue: Offers protection

Ground tissue: Makes up the bulk of the plant, offers support and photosynthesis.

Vascular tissue: Contains xylem to transport water and minerals up the plant, whereas the phloem transports food downwards

What are the two classes of flowering plants

Dicots and monocots.

Dicots

Dicots have two seed leafs / cotyledoms, also for food storage,

Dicot other characteritics

Have a netted or reticulate ventilation

Flower parts arranged in 4/5 or 4/5 multiples.

Vascular bundles arranged in a fixed arrangement around the edge.

Dicot Diagram

Monocots

Monocts have one cotyledon in the seed. The seed leaf is for food storage.

Monocot other characteristcs

Tend to have parallel venation.
Flower parts are in 3 parts or multiples of 3

Monocot diagram

They have vascular tissue, arranged in bundles and organised in a non fixed pattern.

Transection of a dicot root

Dicot root’s vascular tissue is not arranged in bundles. It has a star like xylem with the phloem in between. 

With root hairs to absorb water.

Different types of roots

Fibrous Root System

Tap Roots

Fibrous Root Diagram

Fibrous Root System Details

Grass has fibrous roots and generally are monocots.

Roots formed from the stems, which results in various roots of smaller sizes.

Tap Root Diagram

Tap Roots Details

The tap root forms from the radical in the seed.

This is associated with dicots.

It’s a main larger root with smaller lateral side roots stemming from it.

Longitudinal section of roots ZONES

Section Of Roots Details

• Zone of protection (root caps) protects root as it grows down into the soil.

• Zone of cell production contains meristems that are capable of creating new cells via mitosis

• Zone of elongation is where these new cells get longer

• Zone of differentiation, these elongated cells turn into dermal, ground or vascular tissue

Function of roots

• Anchorage

• Absorb water and minerals

• Transport

• Storage

The longitudinal diagram of root TISSUE

Xylem role

Xylem transports water and dissolved minerals.

Xylem Details

Two forms: 

• Tracheids

• Xylem Vessels

Tracheid Details

Long hollow tubes

Tapered tissue with pointy ends

It contains holes called pits

Overlaps with other tracheids

Xylem Vessles

Wider than tracheids and are tubes

Xylem vessels details

Long hollow continous tube

Vessels are wider than tracheids

Vessels are more effiicent at water transport

Xylem Vessel Structure Diagram

Xylem Tubes Details

1. Hollow Lumen: 

Where water and minerals pass through

2. Pits: 

Where water can flow through and pass sideways

3. Cell walls: 

Thick with spiral of lignin. It’s presence prevents inwards collapse of xylem.

Xylem Details

Classed as dead cells (cells living contents are dead at maturity)

The vessels are hollow tubes which are made up of vessel members - these stack to form the xylem vessel

Lignin is the key to the strength of the xylem

Phloem details

• Made of sieve tubes elements stacked to form sieve tubes.

• Each sieve tube element has a companion cell joined

• Sieve tube elements have plates are at the bottom, with many holes

• Cytoplasm pushed to the sides of every sieve tube element

• Due to the presence of companion cells, it’s considered living tissue.

Phloem longitudinal diagram

Phloem transverse diagram