Plant Science

PLANT SCIENCE

PLANT STRUCTURE AND GROWTH

Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant.

STEM TISSUES:

• Region where leaves are attached to the plant.

• The node is where a leaf joins the stem.

• Epidermis is involved in protection, has pores that allow gas exchange.

• The transporting tissues are the xylem and phloem and are arranged together in a circle. The xylem mainly carries water and dissolved minerals from the roots to the leaves. The phloem transports organic nutrients through the plant.

• The cambium separates the xylem and the phloem.

• The cortex supports and has storage functions.

• Central pith region is a storage and support area.

LEAF TISSUES:

• Leaves are involved in photosynthesis.

• They consist in a flattened portion called the blade and a petiole that attaches the blade to the stem.

• Have a layer of wax; cuticle is the outer layer, which protects against water loss and insect invasion.

• The upper epidermis also protects.

• Vascular tissue which includes xylem and phloem. The xylem brings water to the leaves and the phloem carries the products of photosynthesis to the rest of the plant.

• In the upper portion of the leaf we have the palisade mesophyll with cells with a lot of chloroplasts. Where light is most available.

• The bottom portion is the spongy mesophyll, loosely packed cells with few chloroplasts, there are many air spaces providing gas exchange.

• Stomata are found in the bottom part of the leaves allow O2 and CO2 exchange, guard cells control the opening and closing of stomata.

Outline three differences between the structures of dicotyledonous and monocotyledonous plants.

• Land vascular plants are angiosperms

• These posses flowers

• Flowering plants coevolved with pollinators to allow transfer of the male pollen to the female reproductive organs.

STRUCTURE Monocotyledons Dicotyledons

Number of cotyledons 1 2

Leaf veins Parallel venation Netlike venation

Roots Root system mainly fibrous Root system involves a main root

Floral organs 3 flower parts or multiples of 3 4 or 5

Stem vascular arrangement Vascular bundles arranged throughout the stem Vascular bundles arranged as a ring in the stem

Pollen Pollen grain with one opening Pollen grain with three openings

Explain the relationship between the distribution of tissues in the leaf and the function of these tissues.

Upper Epidermis

 Function: Water conservation (secretes cuticle to create a waxy outer boundary)

 Distribution: On top of leaves where light intensity and heat are greatest

Palisade Mesophyll

 Function: Main photosynthetic tissue (cells contains many chloroplasts)

 Distribution: Upper half of leaf where light intensity is greatest

Spongy Mesophyll

 Function: Main site of gas exchange (made of loosely packed cells with spaces)

 Distribution: Lower half of leaf, near the stomatal pores (where gases and water are exchanged with the atmosphere)

Vascular Tissue

 Function: Transport of water (xylem) and the products of photosynthesis (phloem)

 Distribution: Found in middle of leaf (allowing all cells optimal access)

Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils.

• Extensive modifications of roots, stems and leaves in different types of plant which allow plants growing in varied environments to survive.

ROOTS: Modified roots which serve as food storage and allow the plant to survive in adverse conditions. CARROTS.

STEMS: Bulbs are vertical, underground stems consisting of enlarged bases of leaves that store food. ONIONS.

LEAVES: Tendrils are slim and provide support and attachment, allowing the plants to grow upwards. GRAPE VINES.

State that dicotyledonous plants have apical and lateral meristems. Compare growth due to apical and lateral meristems in dicotyledonous plants.

 Plants may show indeterminate growth because of their meristematic tissue.

 A meristem is a tissue in a plant consisting of undifferentiated cells.

APICAL MERISTEMS:

 Occurs at the tip of roots and stems

 Adds vertical growth to roots and stems, increase in length

 Responsible for primary growth

 Develops into primary xylem and phloem

 Produces new leaves and flowers

LATERAL MERISTEMS:

 Occurs at the cambium

 Adds lateral growth to stem, increase in with

 Responsible for secondary growth

 Produces secondary xylem and phloem

 Produces the bark on trees

Explain the role of auxin in phototropism as an example of the control of plant growth.

 Phototropism is the growing or turning of a plant in response to light

 Auxins, IAA, are plant hormones found in the embryos of seeds that cause a positive phototropism of plant stems and seedlings.

 They increase the flexibility of plant cell walls in young developing stems.

 Auxin accumulates on the shaded part of the plant causing this side only to lengthen, resulting in the shoot to bend towards light.

TRANSPORT IN ANGIOSPERMOPHYTES

Outline how the root system provides a large surface area for mineral ion and water uptake by means of branching and root hairs.

 Plants take up water and essential minerals via their roots and thus need a maximal surface area in order to optimise this uptake

 The monocotyledon root has a fibrous, highly branching structure which increases surface area for maximal absorption

 The dicotyledon root has a main tap root which can penetrate deeply into the soil to access deeper reservoirs of water and minerals, as well as lateral branches to maximise surface area

 The root epidermis may have extensions called root hairs which further increase surface area for mineral and water absorption

 These root hairs have carrier proteins and ion pumps in their plasma membrane, and many mitochondria within the cytoplasm, to aid active transport.

List the ways in which mineral ions in the soil move into the root

WATER:

• It must pass through several regions of the root before it enters the vascular cylinder.

• It moves into the root hairs because they have a higher solute concentration an lower water concentration than the surrounding

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