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Plants and Fungi (3 Major Plants Organs (Leaves: main photosynthetic organ…
Plants and Fungi
3 Major Plants Organs
Shoots: Organ to which the leaves are attached; function is to elongate and orient the shoot in a way that maximizes photosynthesis by leaves and elevates reproductive structures (for wider range of dispersal)
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Apical bud: bud at the tip of a plant stem, also called terminal bud
- composed of developing leaves and series of nodes + internodes
- grow VERTICALLY
Axillary bud: structure that has the potential to form a lateral shoot or branch
- bud appears in the angle formed between leaf and stem
- growth is HORIZONTAL
Leaves: main photosynthetic organ, also responsible for gas exchange, heat dissipation, and defense (against herbivores and pathogens)
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Petiole: joins the blade to the stem
- Note: grasses and monocots usually lack petioles and have the bases of their leaves form sheaths enveloping the stem
Veins: vascular tissue that aids in transporting the supplies for photosynthesis to the leaf and transporting the product of photosynthesis away from the leaf to the rest of the plant
Note: there is much variation of leaf form, some leaves have developed adaptations for specific adaptations to aid in functions like support, protection, storage, and reproduction
Spines: photosynthesis carried out by fleshy green stem, not leaves (cactus)
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Reproductive Leaves: some succulent leaves produce adventitious plantlets that fall off the leaf and take root in the soil (Kalanchoe daigremontiana)
Tendrils: used to cling to for support, some tendrils are modified stems (grapevines or pea plants)
Tissues (4):
Stomata: allows gas exchange (oxygen and carbon dioxide) between environmental air and photosynthetic cells in leaf
- located in epidermis (on both top and bottom of of leaf)
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Roots: Organ that anchors a vascular plant in the soil, absorbs minerals and water, and often stores carbohydrates
Taproot System: one main vertical root called the taproot that penetrates the soil deeply and aids in plant remaining upright (prevents plant from toppling over)
- lateral roots branching from taproot are responsible for absorption
- taproot allows the plant to grow tall (and ultimately stretch above neighboring plants)
Fibrous System: Mat of thin roots spreading out below the surface that connect to the stem (adventitious)
- many roots that spread out allow a wider area of absorption of water
- no taproot present
Root Hairs: thin finger-like extensions of root epidermal cells (present in a large number at the tip of most roots to increase surface area for absorption)
Angiosperm life cycle and reproduction: Flowers, Double-Fertilization, and Fruit
Double-Fertilization: union of two sperm cells with different nuclei of female gametophyte
- one sperm fertilizes egg (to become embryo) and one sperm fertilizes 2 polar nuclei (to become endosperm)
- ensures endosperm develops only in ovules where egg has been fertilized which prevents angiosperms from squandering nutrients on infertile ovules
- endosperm: food storing tissue of the seed
- If pollen grain germinates, a pollen tube grows down the style toward the ovary
- pollen tube discharges two sperm into the embryo sac within an ovule
- one sperm fertilizes egg and forms the zygote
- fertilization of the polar nuclei forms triploid cell that develops into endosperm
Process:
- pollen lands on stigma
- pollen germinates and tube cell begins forming pollen tube
- tube cell lengthens pollen tube
- pollen tube forms around ovary and generative cell splits to form 2 sperm cells
- pollen tube approaches ovule along the bottom of the ovary
- pollen tube penetrates ovule through micropyle, tube cell disintegrates, sperm cells enter ovule
- fertilization of egg, fertilization of endosperm
Seeds: the result of double fertilization!
- each fertilized ovule develops into a seed an each ovary develops into a fruit enclosing a seed
- seed = embryo (diploid) + endosperm (triploid)
- in eudicot plants the endosperm's stockpile is exported to the cotyledons (seed leaves) before the seed completes development
- environmental factors break seed dormancy
- imbibition: the uptake of water by a dry seed which causes the seed to rupture its coat
Pollination: act of placing pollen (containing male gametophyte) on the stigma of a carpel
- male gametophyte will then travel to female gametophyte (inside embryo sacs located inside the ovule)
- plants usually transfer pollen to a different flower
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Biotic pollination: insects, bats, and birds
Self-fertilizing: seen in some crop plants, ensures that every ovule will develop into a seed
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3 Major Plant Tissues
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Dermal: plant's outer protective covering (similar to skin); defense against pathogens and physical damage
Woody plants: have periderm - rather than epidermis in older regions of stems and roots - offers more protection
Non-woody plants: have epidermis (tightly packed cells) and cuticle (waxy coating on epidermal surface to prevent water loss)
Plant Growth:
Note: primary and secondary growth can occur simultaneously AND have indeterminate growth (can grow entire lives)
Primary growth:
- occurs at apical meristems in roots and shoots
- grow in length due to sun and soil exposure
- all plants have primary growth
Apical meristems: occurs in ALL plants (nonwoody and woody)
- at the tip of roots and shoots and axillary buds of shoots
- enable growth in length (producing almost all the plant body in non-woody plants and primary growth in other plants)
Apical Dominance: phenomenon in which an active apical bud inhibits growth from nearby axillary buds
- inhibition is through plant buds
- if the apical bud is removed, the axillary bud will grow a lateral shoot (pruning bushes grows back bushier)
- if the apical bud is removed AND plant hormones are applied at the site of removal, the axillary bud will be inhibited from growing
Secondary growth:
- occurs at lateral meristems (vascular cambium + cork cambium)
- grow in thickness in parts of stems and roots that no longer grow in length
- only woody plants
- increases the diameter of stems and roots
- occurs mostly in eudicots and gymnosperms
- RARELY occurs in monocots
Lateral meristems: occurs only in WOODY plants
- also known as vascular cambium or cork cambium
- enable growth in thickness (secondary growth in woody plants)
- vascular cambium adds layers of vascular tissue (secondary xylem and phloem)
- cork cambium replaces epidermis with the thicker, tougher periderm
Xylem is present in larger amounts in secondary growth because:
- vascular cambium produces more xylem than phloem
- secondary growth is sloughed off as a stem or root increases in circumference
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