introduction to horticulture importance of plants plant parts & their functions
TRANSCRIPT
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Introduction to HorticultureImportance of Plants
Plant Parts & Their Functions
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The Importance of Plants
• Without plants, life on earth could not exist• Plants are the primary source of food for
humans and animals
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The Importance of Plants cont.
• Plants also:– Provide oxygen– Provide shade– Supply us with medicines– Renew the air– Slow down the wind– Hold soil in place– Are a home for wildlife– Furnish building materials and fuel
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Parts of the Plant
• Most plants are made up of four basic parts:– Leaves– Stems– Roots– Flowers (these later
become fruit or seeds)
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Roots
• Usually underground – not visible• Functions:
– Anchor the plant and hold it upright*– Absorb water and minerals from the soil &
conduct them to the stem*– Store large quantities of plant food*– Propagate or reproduce in some plants
* = essential to all plants
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Roots on the Inside
• Very similar to a stem• Older roots of shrubs
& trees have:– Phloem on the outside
(old phloem is bark)– Cambium layer– Xylem (wood) on the
inside
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• Phloem– Carries manufactured food down to the root for food
storage
• Xylem – Carries water and minerals up to the stem
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Roots on the Outside• Different from a stem• On a stem, the
terminal bud
initiates growth• On a root,
the root cap
initiates growth• Root cap continuously
makes new cells that protect the root as it pushes into the soil
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Root External Structure
• Behind the root cap are root hairs
• Root hairs become side roots that branch out as the root grows older
• Absorb moisture and minerals which are conducted up to the larger roots and the stem
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Roots as Crops
• Cash crops– Carrots– Beets– Radishes– Sweet Potatoes
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Root Propagation
• Plants with tuberous roots:– Dahlia– Peony– Sweet Potato
• Are propagated by separating the root clump or by rooting spouts from the root
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Types of Root Systems
Fibrous Root System vs. Tap Root System
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Stems• Stems have 2 main functions:– The movement of
materials • Movement of water and
minerals from roots up towards the leaves
• Movement of manufactured food from the leaves down to the roots
– Support of the leaves and reproductive structures• Flowers and fruit or
seeds
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Stems cont.
• Stems are also used for:
• Food storage– Irish Potato
• Reproductive methods – Stem cuttings or
grafting
• Green stems manufacture food just like leaves
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Stems on the Outside
• Lenticels– Breathing pores
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Stems on the Outside cont.
• Bud scale scars– Indicate where a
terminal bud has been located
– The distance between two scars represents one year of growth
• Leaf scars– Show where leaves
were attached
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Unique Stems
• Irish Potato & Gladiolus – Very different stems– Stems are used for food storage and plant
reproduction
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Stems on the Inside
• In all stems:–Water and
minerals travel up the XYLEM
–Manufactured food travels down the PHLOEM
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Dicots
– Dicots (2 cotyledons - seed leafs) the xylem and phloem are separated by the cambium
– The cambium produces new cells– Grow continually because the cambium builds
new xylem and phloem cells– Trees are a perfect example!
• Sap = new xylem• Heartwood = old, inactive xylem• Tree bark = old, inactive phloem
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Monocots
• One cotyledon (seed leaf)• Grasses, corn• No outside cambium• Vascular bundles that contain xylem &
phloem• Cells don’t increase in number, they grow
in size (won’t keep growing like a tree)
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What do we do with Stems?
• Food– Asparagus– Irish Potato– Celery
• Building Materials– Wood
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• Which root system is easier to transplant? Fibrous roots or tap roots?
• Answer: Fibrous roots
• Why? Because when plants are dug up out of the ground, a greater % of the fibrous roots system is saved.
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• If a root loses to many root hairs while being transplanted, the plant will die.
• Larger roots only conduct & store water, nutrients, and food
• Root hairs absorb moisture from the ground
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Leaves
• Are the food factory of the plant
• They produce all of the food that is used by the plant and stored for later use by the plant or by animals
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Leaves Come in All Shapes and Sizes!• Needles are actually very narrow leaves• The thorns on a cactus are leaves• Some leaves are flat• Other leaves, like onion leaves, are cylindrical• The shape and size of leaves helps to identify
plants
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Leaf Arrangement• Leaves are arranged
in many different patterns and positions:– Alternate– Opposite– Whorled– Compound
• Leaf Composition– Simple– Compound
• Pinnate • Bi-Pinnate• Palmate
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Leaves on the Outside• Parts:
- Petiole - Blade - Vein
- Midrib - Margin
Tip
Midrib
Margin
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Leaf Parts cont.
• Petiole - leaf stalk• Blade - the larger, usually flat part of the
leaf• Midrib - large central vein from which all
other leaf veins extend• Veins - form the structural framework• Margins - edges of plant leaves
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Leaves on the Inside
• Leaves have specialized cells that perform very important, very specific tasks.
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Leaf Cells• Epidermis - skin of the
leaf– Single layer of cells– Chief function: protect the
leaf from loosing too much moisture
– Guard Cells - open and close a small space or pore on the underside of a leaf called a stoma to allow the leaf to breathe (exchange O2 for CO2) and transpire (or give off moisture)
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Leaf Cells cont.
• Chloroplasts– Food making cells– Chlorophyll - green color
• Photosynthesis– Process by which chloroplasts make food– The oxygen created is used directly by people
and animals– Without oxygen there would be no burning,
rusting, or rotting
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6H2O + 6CO2 ----------> C6H12O6+ 6O2
Six molecules of water plus six molecules of carbon dioxide in the presence of light produce one molecule of sugar plus six molecules of oxygen
PhotosynthesisLIGHT
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Plant Food
• Food made in the leaves moves down the stem to the roots
• It is then used by the plant or stored in the roots or stem as sugar, starch, or protein
• The plant is also used as food for people and animals
• The leaves are usually the most nutritious part
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Respiration
• Plants always breathe • They consume oxygen
and release carbon dioxide
• Roots, stems, and leaves all need oxygen to grow
• Plants produce more oxygen during photosynthesis than they consume while breathing
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Flowers, Fruits, & Seeds
• Flowers are pretty & contain nectar in order to attract insects
• These insects fertilize the flower by pollination
• Pollination begins fruit and seed formation
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Fruits & Seeds• Fruits and seeds are eaten, collected, and
spread out by animals and people• This reproduces the plant
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Seeds
• Seeds have special devices to ensure propagation
• Some seeds are sticky (thistles), some float in the wind (dandelions), others can survive stomach acid (cherry pits)
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Flower Parts
• Flowers differ in shape, size, and color, but all have relatively the same parts
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Flower Parts cont.
• Seeds are the most common way plants reproduce in nature – Sexual process involving male and female
parents• A complete flower has both male and
female parts • Only one parent is needed if a plant is self-
fruitful, or can pollinate itself
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Flower Parts cont.
• 4 main parts – Sepals– Petals– Stamens– Pistil
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The Sepals
• Green, leaf like parts of the flower that cover and protect the flower bud before it is open
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Petals
• Are actually leaves• Generally the most striking part of the
flower• Bright colors are used to attract insects for
pollination
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The Stamens• Male reproductive part• Each stamen consists of:
– Filament– Anther – contains the pollen (male sex cell)
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The Pistil
• Located in the center
of the flower• Female part• Produces female sex
cells (eggs or ovules)• If fertilized, the eggs
become seeds
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Parts of the Pistil
• 3 main parts:– Stigma – sticky,
catches the pollen– Style – tube that leads
to the ovary– Ovary – eggs develop
here, after fertilization the ovary grows to become a fruit or seed coat
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Flower Construction
• Insects looking for nectar have to climb over the anther and brush pollen on their legs
• As they climb towards the center looking for food, they deposit pollen on the stigma
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Fertilization
• After an insect deposits pollen, fertilization begins!
• The pollen grain sprouts and sends a long stalk (pollen tube) down the style to the ovary
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Fertilization cont.
• The pollen sperm cell can then fertilize the female egg cells and seeds begin to develop
• The ovary enlarges into a seed coat or fruit
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Pollen
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Incomplete Flower
• Has ONLY male parts or female parts • Male flower – sepals, petals & stamens
but no pistil• Female flower – sepals, petals, & pistil, but
no stamens• Examples: Kiwi, Ginkgo
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Flowers are Important!
• Many plants are grown only for their flowers
• Floriculture industry in a multimillion dollar business!!!
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What is the major function of flowers?
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What is a fruit?• A ripened flower ovary• Botanically, fruits = vegetables
& vegetables = fruits• In most plants, a fruit is
formed following fertilization of the ovules
• They contain seeds
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What about seedless fruit?• Seedless fruit -- fruit that form
without pollination or fertilization• These fruit are called
PARTHENOCARPIC• Examples: Banana, navel
orange
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• When the fruit ripens, the ovary wall thickens.
• This is called the pericarp• The pericarp has three
sections:• The endocarp• The mesocarp• The exocarp
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Types of Fruits• Aggregate fruits
• Multiple fruits
• Simple fruits