Plant Leaves Flashcards
2.51 State the primary function of leaves
The primary function of leaves are
- to photosynthesis, converting energy from sunlight into chemical energy that can be used by the plant
- Transpiration
- Gas exchange
2.52a Describe the structure and state the function of the petiole
Description: Petioles (leaf stalk) are the basal and usually narrowly cyclindrical part of the leaf which carries the vascular bundles and is located between the plant stem and lamina. Petioles vary in legth and may be entirely absent in monocotyledon and sessile (stalkless) leaves
Function: petiole support the lamina away from the stem and transport food made in the leaf to the rest of the plant, and the leaf to receive water and nutrients from the root system
2.52b Describe the structure and state the function of the lamina
Description: lamina is normally the largest and most conspicuous part of a leaf. Typically flat and green the lamina presents the maximum surface area to sunlight so that photosynthesis can occur with greatest efficiency
Function: lamina the site of photosysnthesis and transpiration
2.52c Describe the structure and state the function of the veins
Description: veins strands of vascular tissue in the lamina often visible on the surface of the leaf
Function: veins translocation of water, nutrients,sugarsandplant hormonesto the plant. Additionallysupportof thelamina
2.52d Describe the structure and state the function of the midrib
Description: Midrib (main vein) the main vascular supply and support structure of a simple leaf blade or leaflet, a continuation of the petiole, running the full length of the leaf
Function: midrib is the translocation of water, nutrients, sugars and plant hormones to the rest of the plant. Additionally support of the lamina
2.52e Describe the structure and state the function of leaf shape
Many various different leaf shapes – known by different descriptive names to enable clear identification. Different leaf shapes have evolved to meet the needs of the plants & are a response to their environment. Leaf shapes differ as plants balance the need to photosynthesise (enough sunlight and CO2 to photosynthesis), but not too much associated heat absorption or water loss. Leaf shap can alter within a plant e.g. typically smaller leves higher in a trees canopy to reduce heat absorption, whilst having larger leaves lower in the canopy where it is more shaded
Function: leaf shape useful indicators when trying to identify a plant. Allows the plant to optimise photosynthesis in its habitab
2.52f Describe the structure and state the function of leaf colour
Description: leaf colour is decided by the differing amounts of 3 types of pigments found in leaves; chlorophyll, carotinoids and anthocyanins. Depending on which is most prevalent will determin the leaf colour we see.
Function: Leaf colour helps the plant to optimise photosynthesis. Chlorophyl is the most effecient pigment at enabling photosynthesis, hence it is typically the most prevalent leaf colour. Anthrocyanin and Carotenoids pigments help perform a protective function, stopping the leaf from absorbing too much sunlight this is because Anthrocyanins and Carotenoids are more effecient at absorbing light waves legths that chlorophy does poorly in helping to disapate excess heat energy
e.g. Fagus sylvatica Atropurpurea Group.
2.52g Describe the structure and state the function of leaf arrangement on the stem (simple, compound palmate, compound pinnate)
leaf arrangement on the stem is dependant on water supply and light energy supply in the species habitat
- simple leaves have a continuous leaf blade with an axaillary bud at the base of the petiole. There are mulitiple leaf shapes. Linear leaves are characteristic of monocotyledons
- compound palmate: lamina has 2 or more subunits called leaflets. In compound palmate leaves, the leaflets radiate from a single point at the distal end of the petiole (leaf stalk) the only axaillary bud is located at the base of the main leaft stalk where it attaches to the stem
- compount pinnate: a row of leaflets forms on either side of an extension of the petiole called the rachis. The separate leaflets each with an indivdual base on one leaf stalk, the only axaillary bud is located at the base of the main leaft stalk where it attaches to the stem
2.53 Produce drawing of a dicotyledon leaf section to include:
- epidermis,
- xylem,
- phloem,
- veins,
- palisade
- spongy mesophyll,
- cuticle,
- guard cells
- stomata
insert drawing to include:
- epidermis,
- xylem,
- phloem,
- veins,
- palisade
- spongy mesophyll,
- cuticle,
- guard cells
- stomata
2.53a Describe the structure and state the function of leaf epidermis
Description: leaf epidermis a single layer of cells that covers the leaves, typically transparent. It forms aboundry between the plant and the external environment. The leaf epidermal cells are covered by a waxy layer called the cutical which helps reduce water loss.
The epidermis provides protection against water loss, regulates gas exchange, and baterial attact
2.53b Describe the structure and state the function of leaf xylem
Description: leaf xylem are the woody element of the vascular bundle. They are long wide open ended cells with very thick lignified walls, able to withstand the high pressures of water and solutes
- xylem vesel only have upwards flow
Function: leaf xylem transport water and mineral solutes up from the root system
2.53c Describe the structure and state the function of leaf phloem
Description: leaf phloem are long tube like cells (sieve tubes) They have cellulose walls and are living unlignified cells with no nucleus. The end walls are only partially broken down to leave sieve-like structures (sieve plates) at intervals along the sieve tubes. Each has a companion cell which regulates the movement of water through the sieve tube.
- pholem vessel have two way flow, up and down
Function: leaf phloem allow the transport of food and plant hormones from the leaves to the rest of the plant
2.53d Describe the structure and state the function of leaf veins
Description: leaf veins represent the vascular structure of the organ, extending into the leaf via the petiole. Frequently the veins branch, forming cyclindrical bundles that spead through the middle layer of the leaf, the mesophyll
Function: leaf veins are part of the plants vascular sytem, they translocate food, mineral solutes, water and plant hormones from the leaves to the rest of the plant. Additionally they can help mechanically support the leaf
2.53e Describe the structure and state the function of leaf palisade
Description: palisade cells are located directly below the cuticle and epidermis. They are vertically elongated cells, one to two cells thick, containing many chloroplast organelles
Function: palisade cells are the primary location of photosynthesis in plants
2.53f Describe the structure and state the function of leaf spongy mesophyll
Description: spongy mesophyll cells here are not so tightly packed allong carbon dioxide and oxygen to difuse in and out during photosynthesis and respiration. Significantly fewer chloroplasts than in the palisade layer. Stomata are coonected to the intercelular space betwwen the spongy mesophyll and plisade cells
Function: spongy mesophyll enables the gas exchange needed for photosynthesis and respiration
