All flowering plants are called angiosperms.
All plants are:
- All multicellular
- All photosynthetic
Plants are divided into two groups:
- A cotyledon is an embryonic seed leaf.
During early development of the plant, cotyledons are used as a food source or for photosynthesis (depending on the type of plant).
Monocotyledonous plants have one embryonic seed leaf.
Dicotyledonous plants have two embryonic seed leaves.
Tissue types in flowering plants:
1. Dermal: outer covering – functions in protection, gas exchange or absorption of water and minerals (depending on its location).
2. Ground: makes up the bulk of the plant – functions in photosynthesis, storage or support (depending on its location).
3. Vascular: composed of xylem and phloem tissue – functions in water and mineral transport (xylem) and food transport (phloem).
4. Meristematic: develops into each of the above three types of tissue.
- Meristem: plant tissue composed of rapidly dividing unspecialised cells. These cells are dividing by mitosis.
Structure of the flowering plant
The diagram shows the structure of a typical flowering plant.
All plants are composed of a root system and shoot system.
The shoot system consists of the following organs: stem, branches, petioles, buds, leaves, flowers, seeds and fruits.
Functions of the shoot system include:
- Sexual reproduction
- Food storage
- Gas exchange
Stem functions mainly in support and transport – but can function in photosynthesis (if it is herbaceous). The stem also functions in growth.
The stem is divided into nodes and internodes.
- Nodes are regions where branching occurs.
- Internodes are where no branching occurs.
Stems also have lenticels.
- Lenticels are small pores on a stem that function in gas exchange.
Internal structure of the stem:
The structure of the stem differs between monocots and dicots (see diagrams below – click into each diagram to see a larger view.
- Thin organ with a large surface area.
- Organ that makes food for the plant and functions in transpiration (loss of water from the plant).
- Contains the green pigment, chlorophyll.
- The outer dermal layer secretes a waxy cuticle to prevent excess water loss.
- The leaf contains many internal air spaces that gives greater surface area for gas exchange.
- The cells that make up the upper layer of ground tissue within the leaf contain many chloroplasts that carry out photosynthesis.
- The lower epidermal layer has many pores, called stomata.
- Stomatal opening and closing is controlled by guard cells.
External and internal structure of leaf:
The veins on leaves are of two types:
- The veins run parallel, the entire length of the leaf; e.g. grass, tulip, daffodil.
- Most monocot plants have parallel venation.
- The veins spread out from a central vein called the midrib (see above).
- Most dicot plants have net or reticulate venation.
- A bud is an undeveloped shoot
There are three types of bud:
- Axillary bud: present at the axil of leaf (between the stem and the petiole).
- Apical bud: present at the tip of the plant or the tip of a branch.
- Adventitious bud: present in an unusual area of the plant – such as the stem, branch, root or even leaf.
Flower arrangement between monocots and dicots
- Monocots have flower parts arranged in multiples of three.
- Dicots have flower parts arranged in multiples of four or five.
A network of underground branches that have various functions:
- Absorbing water and minerals
- Transport of absorbed water and minerals to the shoot system
- Storage of food
Types of root system:
- Tap root system: one main root growing downwards with small secondary roots; e.g. carrot, dandelion.
- Fibrous root system: main roots of equal size; e.g. grass.
- Adventitious root system: roots that grow in unusual places such as the stem or branches; e.g. bayan tree, ivy.
There are four zones of a young root.
- Zone of protection: consists of a root cap, enabling the root to push its way through the ground.
- Meristematic zone: consists of meristematic tissue that divides rapidly by mitosis, creating new root tissue.
- Zone of elongation: area of the root affected by growth regulators, where the cells increase in size.
- Zone of differentiation: area of the root where unspecialised cells start to become specialised, becoming ground, dermal and vascular tissues.
The transverse structure of a root is shown below:
The vascular system in a plant is composed of two types of tissue: xylem and phloem.
- A dead tissue – there is no cytoplasm and no nuclei in xylem tissue.
- Contains lignin that gives the tissue high strength.
- Transports water and dissolved minerals upwards.
- Composed of two types of cell: tracheids (structure A in the diagram below) and vessels (structure B in the diagram below).
- A living tissue.
- Transports food (in the form of sucrose) upwards and downwards, depending on where food is needed.
- Composed of companion cells and sieve tube cells.
Mandatory Activity: to prepare and examine microscopically a transverse section of a dicot stem at 100x and 400x.
- Geranium stem
- Backed blade
- Clock glass
- Paint brush
- Glass slide and coverslip
- Light microscope
- Cut a section of stem from an internode of a herbaceous stem such as a geranium.
- Cut a triangular shaped slit along the length of a carrot and place the internode stem into the slit.
- Wet a backed blade and carefully cut (cutting away from fingers) a few sections through the stem and carrot (avoid wedge-shaped sections).
- Transfer the sections to a clock glass of water using a paint brush.
- Place a section on a glass slide with a drop of water (to prevent the section drying out).
- Carefully lower a glass coverslip from a 45º angle (this prevents the formation of air bubbles).
- View the section firstly under low magnification and then under high magnification.
- Make a sketch of each and label.
- Vascular bundles are arranged in a circle with the stem of dicot plants.