plant structure, organization, &...
TRANSCRIPT
Plant Structure, Organization, & Reproduction
Chapter 24/27
Vegetative Organ #1: Roots • Root systems are generally the same size as a plant’s shoot
system (stem and leaves)
• Root systems anchor plants in the ground and provide support
• Roots are typically cylindrical, allowing for easy digging into soil and absorption of water from 360˚.
• Most roots are accompanied by root hairs, small extensions of epidermis which absorb water and nutrients
• Roots are responsible for the growth of plants. They emit growth hormones for the shoot system based on the size of the roots
• If a plant is perennial, plants will store sugars from photosynthesis in their roots for the winter
• Carrots, yams, radishes, etc
Vegetative Organ #2: Stems • Stems are the main axis of plants
• Stems arrange leaves in such a way as to ensure each leaf obtains the most sunlight possible
• Stems have two sections
• Nodes, where leaves attach to stems
• Internodes, space in between the nodes
• Stems transport products of photosynthesis throughout the plant
• In some organisms (such as cacti) the stems are also the primary photosynthetic organ
Vegetative Organ #3: Leaves • Leaves are primarily responsible for photosynthesis
• Because of this, they also play a role in bringing water into plants (particularly from rainwater) and carbon dioxide
• Leaf parts
• Blade: widest portion of foliage
• Petiole: the stalk that attaches the blade to the stem
• Axillary bud: small buds or leafs that emerge from the petiole/node
• See book for a good graph of info comparing monocots and eudicots
Stem Cross Sections
Epidermal Tissue
• Plants have three types of tissue, all of which grow the plant’s entire life because it has meristem (embryonic tissue)
• Epidermal tissue are closely packed cells surrounding plants
• In roots, the epidermis is the root hairs
• In leaves and stems, the epidermis is either cuticle or specialized guard cells surrounding stomata
• In woody plants, the epidermis is replaced by cork, a group of thick, non-living cells that protect the plant from attack from other organisms
Ground Tissue • Ground tissues are all the tissues that fill the interior of the plant
• Parenchyma cells (most abundant ground tissue)
• Contain chloroplasts, carry on photosynthesis
• Undergo the most mitosis out of all ground tissue
• Collenchyma cells
• Flexible covering to provide support for plants
• Strings in celery are collenchyma
• Sclerenchyma cells
• Thick, nonliving material of cell walls,
• Fibrous, such as cotton or flax
Vascular Tissue • Vascular tissues are tissues that transport substances
• This includes xylem and phloem, which we’ve already discussed
• Phloem are organized into sieve tubes which are connected through multiple plasmodesmata to pass nutrients from cell to cell
• Vascular tissue in…
• Roots: vascular cylinder
• Stems: vascular bundles
• Leaves: leaf veins
Root Organization and Diversity
• Root tips contain apical meristem (root embryonic cells) protected by a root cap (a hardened tissue for penetrating the dirt without damaging the root)
• Taproot: fleshy, dominant root of the plant
• Carrot, beet, turnip, radish
• Fibrous root system: slender, lateral branches
• Grasses
• Adventitious roots: roots from the stem above ground
• Corn, mangroves, ivy
• Mycorrhizas: association between roots and fungi for extracting water and nutrients
• Root nodules: extracting nitrogen using bacteria
Woody Stems • Most stems are herbaceous, which means they lack wood
• Woody stems have two tissues, primary and secondary
• Primary growth: increases length
• Secondary growth: increases width
• Bark is a combination of cork, cortex and phloem
• Bark is a protective covering, but also the site of sugar and nutrient transportation
• This is why sap is so easy to access in a tree
Woody Stems • Wood is secondary xylem that builds up year after year
• Xylem in the spring widen to support high levels of water transport
• Later, the xylem will thin when water transport is not as necessary
• (Leaves have fallen or gone into winter hibernation)
• The result is an annual ring in the tree, which shows the combination of thick and thin xylem.
Stem Diversity
• Stolons are above ground, horizontal stems that form new plants where nodes touch the ground.
• Strawberries, grapes
• Rhizomes are underground, horizontal stems
• Contain enlarged portions called tubers, which function in food storage
• Potatoes
• Corms are underground bulb stems
• Onions
Leaf Organization
• Parenchyma cells have many chloroplasts in tightly packed spongy cells.
• The “sponge” effect of leaves allows for increased surface area for gas exchange
• In the center of leaves are veins that contain the vascular tissue for the plant
• In photosynthesis plants REQUIRE water and PRODUCE sugars, so large quantities of xylem and phloem must be present in each leaf (to deliver the water FROM roots and send sugars TO the roots).
Leaf Diversity • Blades of leaves can be simple (one leaflet) or compound
(multiple leaflets)
• Shade plants: broad wide leaves
• Desert plants: reduced, needle-like leaves
• Leaves can
• Overlap: cabbage, lettuce
• Be thick and fleshy: rhubarb, celery
• Climb: peas and cucumbers
• Catch insects: fly trap, pitcher plant
Slide 12
Flowers • Flowers are the reproductive structures of angiosperms
• Peduncle and receptacle: flower stalk, holding the flower parts
• Calyx: protects the flower bud before it opens • Sepals: Green, “leafy” petals below the petals
• Petals: attract pollinators
• Stamens: male parts of the flower • Filament: holds the anther
• Anther: sac that holds the pollen
• Carpel: female parts of the flower • Ovary: the female gametes of the flower
• Style: extension from the ovary holding up the stigma
• Stigma: sticky receptor for pollen
Flowers
• Flowers produce two types of spores in their sporophyte generation
• Microspores, which develop into male gametophytes (pollen)
• Megaspores, which develop into female gametophytes (eggs)
• (Even though it looks like the flower gives way directly to pollen and eggs, an entire generation has occurred within these structures)
• Flowers develop due to environmental signals such as length of the daylight and temperature
• Flowers that have sepals, petals, stamens and a carpel are considered to be complete.
• Flowers that are missing at least one section are incomplete
• Flowers can be bisexual (each flower contains both stamens and carpels) or unisexual (the flower contains either stamens or carpels).
Flowers
• Single plants may possess either male only gametophytes, female only gametophytes, or both.
• If a plant contains unisexual staminate flowers and carpellate flowers, it is called monoecious
• Birch trees, pine trees, corn plants
• If a plant contains either staminate flowers or carpellate flowers, it is dioecious
• Holly trees, Hempaceae
Production of Male Gametophyte
• Microspores are produced in the anthers of flowers
• An anther has four pollen sacs, each with multiple microsporocytes (microspore mother cells)
• Pollen grains eventually develop from these microspores.
• When pollen grains are ready to be released, the walls of the pollen sacs break down and pollination occurs
• Pollination is the transfer of pollen from an anther to stigma
• Plants often have adaptations that synchronize maturity of carpels and stamens at the same time
• Doesn’t do any good to release pollen if the eggs aren’t mature yet
• Pollen is transferred to stigmas by organisms, wind, or gravity
Fertilization
• When a pollen grain lands on the stigma of the same species, it germinates, forming a pollen tube.
• The pollen tube reaches the micropyle of the ovule and double-fertilization occurs
• Each pollen contains two sperm nuclei
• One sperm nucleus unites with the egg nucleus and forms the 2n zygote • This zygote divides mitotically to become an embryo
• The other sperm nucleus migrates and unites with a central cell and forms a 3n cell. • The cell divides mitotically to become endosperm, the tissue that
nourishes the embryo and seedling during development
Fruits
• Fruits protect and help disperse gametes.
• Simple fruits derive from simple ovaries of a single carpel or from a compound ovary of several fused carpels
• Legumes and grains, although they look like seeds, are dry fruits. Dry because they have a dry pericarp (shell)
• Peas, wheat, rye
• Some dry fruits, such as clover or cocklebur, disperse by attaching to fur of animals.
• Some have air sacs enclosed within the seeds which help them float on water (cranberries, coconuts)
• Other dry seeds, such as plumes and wings, are dispersed by wind
• Dandelions, Maples
Fruits • Other fruits develop a fleshy mesocarp. Fleshy fruits attract animals and
provide them with food.
• Peach, tomato, cherry
• The pericarp on these seeds protects the embryos from the animals digestive systems
• Because the seeds are small and flexible, they’re rarely crushed by chewing or digesting either
• Upon defecating the seeds, the waste of the animals provides nutrients for the seeds
• Accessory fruits are fruits built from the receptacle of a flower, not the ovary.
• Apple
• Aggregate fruits are the result of several fused carpels
• Strawberry, raspberry, blackberry
• Multiple fruits are the result of multiple ovaries fusing together.
• Pineapple
Seed Germination • The embryo is dormant inside a seed until seed germination
occurs
• The length of time seeds can remain dormant varies
• Maple seeds: 1 week
• Lotus seeds: centuries
• Some seeds even require a period of dormancy, where no growth occurs even though conditions allow for it.
• Desert plants
• This helps ensure seeds do not germinate until an extended period of favorable conditions occur, not a random moment
• The environmental requirements for seed germination are
• Availability of oxygen for increased metabolic needs
• Adequate temperature for enzymes to act
• Adequate moisture for hydration of cells
• Light (in some plants)
