1. 3/30 – 4/1
Notes on Plant’s structure and functions including hormones and responses
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2. Plant Cells Parenchyma Cells
Most flexible, thin-walled cells found throughout the plant are parenchyma cells.
Can undergo cell division when mature, allowing them to repair damaged parts of plants.
Basis of many plant structures and functions, including:
Storage
Photosynthesis
Gas exchange
Protection
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Plant Cells and Tissues

3. Plant Cells Collenchyma Cells
Plant cells that often are elongated and occur in long strands or cylinders that provide support for the surrounding cells are collenchyma cells.
Have unevenly thickened cell walls, which allow the cells to stretch and be flexible.
Retain the ability to undergo cell division when mature.
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Plant Cells and Tissues

4. Plant Cells Sclerenchyma Cells
Plant cells that lack cytoplasm and other living components when they mature, leaving thick, rigid cell walls are called sclerenchyma cells.
Sclerenchyma cells provide support for the plant and transport of materials.
Classified as either sclereids or fibers
Sclereids are also called stone cells, short and irregularly shaped
Fibers are needle shaped, when stacked together they form a tough elastic tissue
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Plant Cells and Tissues

5. Plant Tissues
Tissues are groups of cells that work together to perform a function.
A plant tissue can be composed of one or more types of cells.
There are four different tissue types found in plants – meristematic, dermal, vascular, and ground.
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Plant Cells and Tissues

6. Plant Tissues Meristematic tissue
Meristematic tissues make up meristems, or regions of rapidly dividing cells which produce new cells for plants.
Apical meristems: tissues at the tips of roots and stems, responsible for primary growth
Intercalary meristems: found at one or more location along a monocot stem
Lateral meristems: increase root and stem diameter through secondary growth
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Plant Cells and Tissues

7. Plant Tissues Meristematic tissue
The vascular cambium is a thin cylinder of meristematic tissue.
Can run the entire length of roots or stems
Some plants also have a type of lateral meristem called the cork cambium.
Produces cells that form a protective outside layer on stems and roots.
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Plant Cells and Tissues

8. Plant Tissues Dermal tissue – the epidermis
The layer of cells that makes up the outer covering on a plant is the epidermis.
Epidermal cells resemble pieces of a jigsaw puzzle with interlocking riges and dips.
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Plant Cells and Tissues

9. Plant Tissues Dermal tissue – the epidermis
The epidermis has several adaptations to protect the plant and prevent water loss.
Changes in the shape of guard cells result in the opening and closing of a stomata.
Some epidermal cells have hairlike projections called trichomes, which prevent insect and animal predation.
Root hairs are fragile extensions of root epidermal cells
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Plant Cells and Tissues

10. Plant Tissues Vascular tissue
Xylem is the water-carrying vascular tissue, composed of specialized cells called vessel elements and tracheids.
Vessel elements are tubular cells stacked end-to-end
Lack end walls, allowing free movement of water from one vessel element to another
Tracheids are tubular cells with pitted ends and end walls.
Less efficient at moving water than vessel elements
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Plant Cells and Tissues

11. Plant Tissues Vascular tissue
Phloem is the main food-carrying tissue in vascular plants
Consists of two types of cells, sieve tube members and companion cells.
Sieve tube members contain cytoplasm but lack nuclei and ribosomes when mature.
Companion cells occur next to sieve tube cells and have a nucleus.
Scientists hypothesize that the companion cell nucleus functions for both cells.
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Plant Cells and Tissues

12. Plant Tissues Ground tissue
Plant tissues that are not meristematic, dermal, or vascular tissues are ground tissues.
Consists of parenchyma, collenchyma, and sclerenchyma cells
Functions include photosynthesis, storage, and support
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Plant Cells and Tissues

13. Roots
The root is usually the first structure to grow out of the seed when it sprouts.
Roots take in water and dissolved minerals that are transported to the rest of the plant.
Roots also anchor plants to the soil or other object.
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Roots, Stems, and Leaves

14. Roots Root structure and growth
The tip of a root is covered by the root cap.
The root cap consists of parenchyma cells to help protect root tissues as the root grows
Root caps are coated in a slimy substance that reduce friction as the root grows through the soil.
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Roots, Stems, and Leaves

15. Roots Root structure and growth
The layer between the epidermis and vascular tissue is the cortex.
Composed of ground tissue paranchyma cells that transport or store substances.
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Roots, Stems, and Leaves

16. Roots Root structure and growth
The inner boundary of the cortex is a layer called the endodermis.
Each cell of the endodermis is encircled by a waterproof strip called the Casparian strip.
The Casparian strip forces water and substances to pass through the endodermal cells instead of around them.
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Roots, Stems, and Leaves

17. Roots Root structure and growth
Directly next to the endodermis toward the center of the root is called the pericycle, which produces lateral roots.
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Roots, Stems, and Leaves

18. Roots Types of roots Two major types: taproots and fibrous roots
A taproot system consists of a thick root with few smaller, lateral-branching roots.
Used for food storage (beets, carrots)
Used for deep growth to reach water
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Roots, Stems, and Leaves

19. Roots
Types of roots
Fibrous root systems have numerous branching roots that are about the same size and grow from a central point.
Other root types are adapted to diverse environments
Pneumatophores are adapted to supply oxygen to roots submerged in water.
Adventitious roots form unusual support structures.
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Roots, Stems, and Leaves

20. Stems Stem structure and function
Some stems are soft, flexible, and capable of photosynthesis – herbaceous stems
Other stems are rigid and fibrous – woody stems
Main function is support of leaves and reproductive costumes
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Roots, Stems, and Leaves

21. Stems
Growth of a stem
The apical meristem produces cells that increase the length of a stem.
As plants grow taller, an increase in stem diameter provide additional support.
The vascular cambium produces additional cells to increase stem diameter
These cells form annual grown rings in some plants, particularly trees, which can be used to age the organism.
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Roots, Stems, and Leaves

22. Stems Types of stems Stems have adaptations that help plants survive
Store excess food
Withstand drought, cold, or heat
Some plants have underground stems (tubers, bulbs, rhizomes)
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Roots, Stems, and Leaves

23. Leaves
Leaf Structure
The main function of leaves is photosynthesis, and they have many adaptations to optimize this purpose
Most leaves have a flattened portion called the blade with a large surface area.
The blade is attached to the stem by a stalk called a petiole.
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Roots, Stems, and Leaves

24. Leaves
Leaf structure
The internal structure of most leaves is well-adapted for photosynthesis.
The palisade mesophyll is composed of tightly packed cells with many chloroplasts.
The spongy mesophyll consists of irregularly shaped cells with spaces in between, allowing gases move between the spaces
Roots, Stems, and Leaves
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25. Leaves Gas exchange and transpiration
The epidermis contains stomata, pores that allow for gas exchange.
Stomata are important in the transportation of water from the roots through the vascular tissue.
Water evaporates through the stomata in a process called transpiration that helps pull the water column upward.
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Roots, Stems, and Leaves

26. Leaves Characteristics of leaves
Leaves differ in size, shape, arrangement on the stem, and venation
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Roots, Stems, and Leaves

27. Leaves Leaf modifications Leaves have functions beyond photosynthesis.
In cacti, leaves have been modified into spines to prevent predation by animals.
Pitcher plants modify leaves into cylinders that fill with water and trap insects.
Some leaves produce toxic chemicals to deter predation.
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Roots, Stems, and Leaves

28. Plant Hormones
Hormones are organic compounds that are made in one part of an organism and affect another part of the organism.
Plant hormones can affect cell division, growth, or differentiation.
Plant hormones work by chemically binding to the plasma membrane and activating receptor proteins, which affect the expression of a gene, enzymes, or membrane permeability.
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Plant Hormones and Responses

29. Plant Hormones
Auxin
Auxin is produced in the apical meristems, buds, young leaves, and other rapidly growing tissues.
Stimulates lengthening or elongation of cells
Results in apical dominance, where plants grow mostly upwards with few side branches
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Plant Hormones and Responses

30. Plant Hormones Gibberellins
Gibberellins causes cell elongation, stimulate cell division, and affect seed growth.
Dwarf plants often lack the genes for gibberellins production or gibberellins receptor proteins.
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Plant Hormones and Responses

31. Plant Hormones Ethylene Ethylene is the only known gaseous hormone.
Affects the ripening of fruit, senescence of leaves
Travels through the phloem as well as the space between cells
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Plant Hormones and Responses

32. Plant Hormones Cytokinins
Cytokinins induce growth in rapidly dividing cells.
Promote cell division by stimulating the production of the proteins needed for mitosis and cytokinesis
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Plant Hormones and Responses

33. Plant Responses Nastic responses
A plant response that causes movement independent of the direction of the stimulus is called a nastic response.
Not a growth response, is reversible, and can be repeated
Opening of leaves during the day, closing of leaves at night
Closing of a Venus flytrap’s leaves
Once the stimulus ends, the leaves return to their original position.
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Plant Hormones and Responses

34. Plant responses Tropic responses
A tropism is a plant’s growth response to an external stimulus.
If a plant grows towards the stimulus, it is a positive tropism
If a plant grows away from the stimulus, it is a negative tropism
Phototropism: growth in response to light
Gravitropism: growth in response to gravity
Thigmotropism: growth in response to mechanical stimuli, such as contact with an object, organism, or wind
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Plant Hormones and Responses