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Ch 7: Leaves - Coggle Diagram
Ch 7: Leaves
Internal Structures
Veins- found within leaves are veins or bundles of vascular tissues. Veins distribute water from the stem into the leaf and simultaneously collect sugars produced by photosynthesis and carry them to the stem for use or storage elsewhere.
In basal angiosperms and eudicots, veins occur in a netted pattern called a Reticulate Venation
In monocots with long strap-shaped leaves, the larger veins run side by side with few obvious interconnections called Parallel Venation
Of Foliage leaves
Transpiration- Water loss through the epidermis when soil is too dry due to not being able to replace the water.
in many species there is no stomata at all found in the upper epidermis. This is beneficial due to the density of air-borne spores of fungi and bacteria are continually landing on leaves. rye leaves typically have 10,000 fungal spores per square centimeter.
Leaf epidermises are often hairy and trichromes affect leaf biology in numerous ways. they provide some shade of the upper surface of the leaf, deflecting excessive sunlight, an adaptation common in desert plants.
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Vascular Tissues
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Bundle Sheath- fibers arranged as a sheath. the sheath also makes it difficult for insects to chew through
Vascular tissues are the most variable; 1, 3, or 5 or more vascular bundles, called Leaf Traces, branch from stem vascular bundles and diverge toward the petiole.
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Leaf Adaptations
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Bud Scales- In perennial plants, dormant shoot shoot apical meristems are protected from low temperatures and the drying action of wind during winter by bud scales, which form a tight layer around the stem tip.
Cactus Spines
these spines are modified leaves of axillary buds. the moist cactus body would be an excellent source of water for animals were it not for these protective spines.
Tendrils
Peas, cucumbers, and squash have these. Tendrils grow indefinitely and contain cells that are capable of sensing contact with an object. When the tendril touches something, the side facing the object stops growing but the other side continues to grow.Instead of responding to light, tendrils respond by sensing solid objects and growing around them.
External structure
What leaves can't do/be
Water loss- through transpiration water loss can be reduced by closing the stomata in the leaves using a substance called ABA. However, by closing the stomata the plant can't take in as much CO2 which means less photosynthesis. This then means less energy so the plant can't grow.
Leaves should not be nutritious or taste good in order to deter animals from eating them. Plants also have other ways to stop predators such as thornes or by producing oils such as in poison ivy.
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Must not be resourcefully expensive. Must not spend more carbohydrates on photosynthesis than on growing.
Must not allow invasion of fungi, bacteria, or epifolior algae
Photosynthesis
Due to the positions of the sun, it is best for leaves to have flat and wide areas for maximum surface area to absorb light and CO2.
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Types of Leaves
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Monocots- have long leaves that also don't need a petiole only self-shade at the base. ex: grasses, irises, lilies etc. leaf base wraps around stem to form a sheathing leaf base
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Insect traps
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Venus Fly Traps have leaves that are held flat. Position is maintained by motor cells along the upper side of the midrib that are extremely turgid and swollen.
How it works- An insect walks across the trap and brushes the trigger hairs. If 2 of these are simulated, midrib motor cells lose water quickly and the trap closes rapidly. Glands secrete digestive fluid that will absorb the insect. Then, the trap resets by the midrib motor cells filling back up with water and swelling open.
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Leaves and their taste
Humans eat many leafy foods such as cabbage, spinach, herbs, thyme, mint, and peppermint all the time. How do they get their flavors?
These flavors and the pungency of them can be found in the leaf or in trichromes of the leaf epidermis. They are most likely supposed to help ward off any herbivores from ingesting them.
Although humans do/ can eat some leaves. Some leaves are still incredibly toxic for humans to ingest. Tobacco Leaves, if eaten, can cause vomiting and even death. Instead of ingesting tobacco leaves, people smoke them
Humans and tobacco- the nicotine in tobacco leaves is addictive and can cause many bad side effects. Nicotine works by dissolving into our mucous membranes then passes into our blood stream. Women who smoke while pregnant can hurt their children by making them come out of the womb addicted to nicotine. People who smoke a pack of cigarettes a day are at a 3x greater risk of dying from heart disease than those who don't smoke.