Plant Structure Flashcards
B3.1.7; B3.1.8; B3.2.9; B3.2.10 (19 cards)
Summarize the 5 key adaptations of leaves for gas exchange.
Waxy Cuticle: Reduces water loss but restricts gas diffusion.
Epidermis: Protects internal tissues while allowing light to pass through.
Stomata and Guard Cells: Regulate the entry and exit of gases and water vapor.
Spongy Mesophyll: Provides a large, moist surface area for gas exchange.
Veins: Supply water and nutrients while transporting sugars away.
What is the role of the waxy cuticle?
- It acts as a hydrophobic barrier to reduce water loss by evaporation.
- Its low gas permeability is balanced by specialized structures like stomata.
What are stomatal pores and where are they typically found on a leaf?
Tiny pores on the lower epidermis of a leaf that facilitate the exchange of respiratory gases and water vapour. They are on the underside of the leaf to prevent obstruction and maintain an open channel for gases.
What is the role of guard cells in stomata?
Guard cells control the opening and closing of stomata, adapting to environmental conditions to minimize water loss.
Describe the spongy mesophyll and its function in gas exchange.
- A loosely packed layer with air spaces to increase the surface area for gas diffusion.
- Moist cell walls allow gases to dissolve, aiding efficient diffusion.
What are veins in leaves composed of and what roles do these structures have?
Veins in a leaf are composed of vascular tissues:xylem and phloem.
These structures play an indirect but vital role in gas exchange:
Xylem: transports water from the roots to the mesophyll cells, maintaining the moist surface required for efficient gas diffusion.
Phloem: carries away the sugars produced during photosynthesis, ensuring the plant has the energy to sustain its metabolic processes.
The interior of a leaf is composed of a layer of tissue called the mesophyll – which is organised into two sections. What are they and what are their roles?
The cells of the palisade mesophyll are tightly packed and rich in chloroplasts (optimised for photosynthesis).
The cells of the spongy mesophyll are loosely packed between intercellular air spaces (maximising gas exchange).
What is the epidermis in leaves?
A transparent layer that protects the leaf and allows sunlight to pass through to photosynthetic tissues.
The transparency of the epidermis is crucial for allowing maximum sunlight to reach the chloroplast-rich cells below, ensuring efficient photosynthesis.
How are the tissues in a leaf distributed to maximise the processes of photosynthesis and gas exchange?
The waxy cuticle covers the exterior surface in order to prevent water loss from the leaf (except via stomata).
The palisade mesophyll is located on the upper half of the leaf (facing sunlight) to maximise light absorption.
The spongy mesophyll is located on the lower half (near stomata) and contains air spaces for gas exchange.
The stomata are on the underside of the leaf to prevent obstruction and maintain an open channel for gases.
The vascular bundle is located centrally to allow for optimal access by all leaf tissue (palisade and spongy).
What are fibrous roots in dicotyledonous plants?
Thin and very spread out to improve absorption, but are not very effective at anchorage (more suitable for smaller plants).
What are tap roots in dicotyledonous plants?
Possess a deeply penetrating main root with many lateral branches (can access deeper soil layers and provides better anchorage).
Name the three main tissue layers in roots and their roles.
- The outer epidermis; where water and minerals enter the roots and may have protrusions (root hairs) to maximise surface area.
- The middle layer (cortex) facilitates water movement between loosely packed cells and also functions as a storage site for starch.
- The innermost layer is the vascular tissue (phloem and xylem), which allows for the transport of materials to other parts of the plant.
Name the 7 key fetures of a dicot root.
Epidermis - Outermost protective layer.
Root Hairs - Extensions of the epidermis for nutrient absorption.
Cortex - Between the epidermis and vascular bundle.
Endodermis - A layer of tightly packed cells surrounding the vascular bundle (may or may not be visible depending on magnification).
Vascular Bundle (Central Cylinder) - Contains the xylem and phloem in a star-shaped arrangement.
Xylem - The central part of the vascular bundle, responsible for water transport.
Phloem - Surrounds the xylem, responsible for transporting sugars.
What are the root hairs in a dicot root, what is their structure and function?
Root hairs extend from some cells to massively increase surface area for absorption.
Root hairs are short-lived but vital for maximizing water and nutrient uptake.
What is the Casparian strip in the cortex of a dicot root?
The vascular bundle is surrounded by cells with a modified cell wall (casparian strip) that is impermeable to water.
This forces water to move into the cells to access the vascular bundle, facilitating greater control of water movement.
What are the three main tissue layers of stems, organised to optimise the transport of water and nutrients between leaves and roots?
Epidermis: Outer protective layer; may have a cuticle.
Cortex: Region between epidermis and vascular bundles; involved in storage and support.
Vascular Bundles: Composed of xylem and phloem.
What is the location, function and structure of the epidermis in dicot stems?
Location: Outermost layer of cells, forming the skin of the plant.
Function: Protects the plant from physical damage, prevents water loss, and acts as a barrier to pathogens.
Structure: Single layer of cells, often with a waxy cuticle on the surface to reduce water loss.
What is the location, function and structure of the cortex in dicot stems?
Location: Just beneath the epidermis, surrounding the vascular bundles.
Function: Primarily serves as storage of starch and other nutrients. It also provides some structural support to the stem.
Structure: Composed of loosely packed parenchyma cells, with some collenchyma and sclerenchyma cells for support.
What is the location, function and structure of the vascular tissue in dicot stems?
Location: Found scattered throughout the stem, arranged in a ring in most dicotyledons. Each bundle contains xylem and phloem.
Function: Vascular bundles transport water, minerals, and nutrients throughout the plant and also support the stem.
Structure: Each bundle is composed of xylem (on the inner side) and phloem (on the outer side), with a cambium layer in between, which is responsible for the plant’s secondary growth.
