1. Chapter 23

2. Specialized Tissues in Plants
Section 23.1
Specialized Tissues in Plants

3. Seed Plant Structure
What are the three principal organs of seed plants?
The cells of a seed plant are categorized by different tissues, organs, and systems.
Roots, stems, and leaves are the three principal organs of seed plants.
The roots, stems, and leaves are linked together by systems that run throughout the plant.
Those systems produce, store and transport nutrients, providing also physical support and protection.

4. Roots
Roots help plants have physical support while holding soil in place to prevent erosion.
Root systems often work with soil bacteria and fungi in mutualistic relationships to help the roots absorb water and dissolved nutrients.
Roots transport things like water and dissolved nutrients throughout the plant.
Roots also store food and hold plants up to support them throughout wind and rain.

5. Stems Plant stems support the plant body so it can be held upright.
Stems have a transport system that carry nutrients, as well as a defensive system to protect a plant from predators and diseases.
Stems produce reproductive organs (i.e. flowers), and leaves.
The stem’s transport system contains tissues that allow it to lift water from the roots to its leaves and carry products of photosynthesis from leaves back to the roots.

6. Leaves Leaves are plants main photosynthetic organs.
Leaves increase the amount of sunlight a plant absorbs depending on the size of its surface.
Leaves also expose tissue to the dryness of the air which then means the plant can have adaptations to protect from water loss.
Leaves also have adjustable pores to help conserve water while letting oxygen and carbon dioxide enter and exit the leaf.

7. Plant Tissue Systems
What are the primary functions of the main tissue systems of seed plants?
The three main tissue systems are dermal, vascular, and ground.
Dermal tissue covers a plant almost like skin covers a human.
Vascular tissue makes a system of pipe like cells to support a plant and serve as a “bloodstream,” by transporting the water and nutrients.
Ground tissue produces and stores food.

8. Dermal Tissue In young plants, dermal tissue consists of an epidermis.
Dermal tissue is the protective outer layer of a plant.
In older plants, dermal tissue is cell layers deep and can be covered in bark.
In roots, dermal tissue includes root hair cells that help absorb water.

9. Vascular Tissue
There are two kinds of vascular tissue, called the xylem and phloem.
Vascular tissue supports the plant body and transports water and nutrients throughout the plant.
Xylem is a water conducting tissue.
Phloem is a tissue that carries dissolved food, but both the xylem and phloem consists of long, slender cells that connect almost like sections of pipe.

10. Ground tissue Ground tissue is also called plant tissue.
It is neither dermal nor vascular.
It stores sugars and produces them, and helps the physical support of the plant.
There are three main cells ground tissue may consist of. Parenchyma cells, which have thin cells walls, Collenchyma cells with thicker cell walls, or Sclerenchyma cells with thickest cell walls.

11. Plant growth and Meristems
How do meristems differ from other plant tissues?
Meristems are tissues.
They are regions of unspecialized cells in which mitosis produces new cells that are ready for differentiation.
Meristems are found in the tips of stems and roots.
The cells that they produce are much like the stem cells of animals.

12. Apical Meristems
Apical meristems get their name because the tip of a stem or root is known as its apex.
Within apical meristems are unspecialized cells that are produced by mitosis.
The new stems that push out of meristems look unspecialized and have thin cell walls.
Gradually they then develop to mature cells with specialized structures and functions, this process is called differentiation.

13. Meristems and Flower Development
Meristems also reproduce the reproductive organs of seed plants.
When the pattern of gene expression changes in a stem’s apical meristem in a flower or cone development, the apical meristem of a flowering plant transform into a floral meristem.
Floral meristems produce tissues of flowers.
The floral meristems also include the plant’s reproductive organs as well as the color of the petals that surround them.

14. Section 23.2
Roots

15. Root Structure and Growth
What are the main tissues in a mature root?
At first when a seed just begins to sprout, the first root draws water and nutrients from the soil.
Other roots then branch out from the first main root, adding length and surface area to the root system.
Rapid cell growth pushes the tips of those growing roots into the soil.
Those new roots provide as raw materials for the developing stems and leaves before coming out of the soil.

16. Types of Root Systems There are two main kinds of root systems.
There are taproot systems and fibrous root systems.
Taproot systems are found usually in dicots.
Fibrous root systems are usually found in monocots.
Dicots and monocots are two categories of flowering plants.

17. Anatomy of a Root
Roots contain cells from the dermal, vascular, and ground tissue systems.
A mature root has an epidermis and contains vascular tissue and a large area of ground tissue.
The root system helps with water and mineral transport.
The cells and tissues of a root are specialized to help with the water and mineral transport.

18. Root Functions What are the different functions of roots?
Roots help absorb water and transport minerals from the soil.
Roots also help to support a plant.
Roots anchor a plant to the ground.
Roots store food as well, and absorb water and dissolved nutrients from the soil.

19. Uptake of Plant Nutrients
Soil holds most of the nutrients that are needed for a plant.
The nutrients needed in large amounts are nitrogen, phosphorus, potassium, magnesium, sulfur, and calcium.
Trace elements that are needed are iron, zinc, molybdenum, boron, copper, manganese, and chlorine.
Excessive amounts of trace elements can be poisonous to plants and have results of deficiency.

20. Active Transport of Dissolved Nutrients
Cell membranes of root hairs and the root epidermis has active transport proteins.
Active transport is a process that uses the energy of ATP to move ions and other materials across membranes.
Active transport brings the mineral ions from dissolved nutrients to the plant from soil.
High concentration of mineral ions in plant cells causes water molecules to move into the plant by osmosis.

21. Water movement by Osmosis
Osmosis is the movement of water across a membrane toward an area where the concentration of dissolved material is higher.
By using active transport to move ions from the soil, cells of the root epidermis make conditions where osmosis causes water to follow the ions making it flow into the root.
The end result is that the root absorbs water and dissolved nutrients from soil.
Although, the root does not actually pump the water.

22. Movement into the Vascular Cylinder
Once the roots has absorbed water and nutrients from the soil, the water and dissolved nutrients pass the inner boundary of the cortex and move toward the vascular cylinder.
The cylinder is enclosed by a layer of cortex cells called the endodermis.
Where the cells meet, their cell walls form a special waterproof zone called the Casparian strip.
The strip enables the endodermis to filter and control water and dissolved nutrients that enter the cylinder, and as a result, there is a one-way passage for water and nutrients into the vascular cylinder.

23. Root Pressure
The root pressure system is how the plant generates enough pressure to move water out of the soil and up into the body of the plant.
Root pressure forces water through the vascular cylinder and into the xylem.
It is the starting point for the movement of water through the vascular system of the entire plant.
Root pressure is important, without it, a plant would not be able to function properly.

24. Section 23.3
Stems

25. Stem structure and Function
What are the three main functions of stems?
Above ground stems have several functions.
Above ground stems produce leaves, branches, and flowers.
Stems hold leaves up to the sun to produce photosynthesis.
Stems transport substances throughout the plant.

26. Anatomy of a Stem Stems contain dermal, vascular, and ground tissue.
Growing stems contain nodes, where leaves are attached.
The nodes attach to buds, which can produce new stems or leaves.
In larger plants, stems develop woody tissue that helps support leaves and flowers.

27. Vascular Bundle Patterns
Vascular bundles are clusters of xylem and phloem tissue.
Vascular bundles are scattered throughout the stem in monocots.
In most dicots and gymnosperms, vascular bundles are arranged in a cylinder (ring).
The arrangement of the vascular bundles differs among seed plants.

28. Growth of Stems How do primary and secondary growth occur in stems?
The growth of plants is not precisely determined compared to animals.
Plant growth is still carefully controlled and regulated, however.
Depending on the plant species, plant growth follows general patterns that produce characteristic size and shape of the adult plant.

29. Primary Growth Primary growth occurs at the end of a plant.
Primary growth of stems is the result of elongation of cells produced in the apical meristem.
Primary growth takes place in all seed plants.
Primary growth is a pattern of growth.

30. Secondary Growth
When plants grow larger, the older stems and roots have more mass to support and more fluid to move through their vascular tissues.
As a result, the plant’s stems and roots increase in thickness and in length.
This increase in the length and width of stems and roots is known as secondary growth.
Secondary growth is common in dicots but not in monocots.

31. Growth from the Vascular Cambium
When secondary growth begins, the vascular cambium appears as a thin, cylindrical layer of cells between clusters of vascular tissue.
This new meristem forms between xylem and phloem of each vascular bundle.
Divisions in the vascular cambium give rise to new layers of xylem and phloem.
As a result, the stem becomes wider.

32. Formation of Wood
Wood is actually secondary xylem produced by the vascular cambium.
These cells build up year after year, making many layers.
As the woody systems gets thicker, the older xylem near the center of the stem no longer conducts water and becomes known as heartwood.
Heartwood is surrounded by sapwood, which is active in fluid transport and is usually lighter in color.

33. Tree Rings
Each tree ring has light wood at one edge and dark wood at the other.
By counting the tree’s rings, you can estimate the edge of a tree.
The size of the rings may also indicate the weather conditions the tree has been through.
Thick rings indicate that weather conditions were favorable for tree growth.

34. Formation of Bark
All of the tissues found outside of the vascular cambium make up the bark.
The tissues that help make up bark include phloem, the cork cambium, and cork.
As a tree expands in width, so must the phloem layer.
As the stem increases in size, outer layers of dead bark often crack and flake off the tree.

35. Section 23.4
Leaves

36. Leaf structure and Function
How is the structure of a leaf adapted to make photosynthesis more efficient?
The structure of a leaf is made to absorb light and carry out photosynthesis.
Leaves have a way to obtain carbon dioxide and water.
Leaves help distribute end products.

37. Anatomy of Leaves
Leaves have blades which maximize the amount of sunlight it can absorb for the rest of the plant.
The blade is attached to the stem by a thin stalk.
The thin stalk is called petiole.
Leaves have an outer covering of dermal tissue and inner regions of ground and vascular tissues.

38. Photosynthesis
Beneath the upper epidermis is palisade mesophyll, containing closely packed cells that absorb light that enters the leaf.
Beneath the palisade layer is spongy mesophyll, which has many air spaces between its cells.
The air spaces connect with the exterior through stomata.
Stomata allows carbon dioxide, water, and oxygen to diffuse into and out of the leaf.

39. Transpiration Transpiration is the loss of water through leaves.
Transpiration may be replaced by water drawn into the leaf through xylem vessels in the vascular tissue.
Transpiration helps to cool leaves on hot days.
Transpiration is also life threatening on days when water is scarce.

40. Gas Exchange and Homeostasis
What role do stomata play in maintaining homeostasis?
Stomata helps control the intake and outtake of plant’s oxygen and water so they are not smothered.
Without control, the plant can suffocate.
Plants can suffocate from lack of oxygen such as in extensive flooding.

41. Gas Exchange
Leaves take in carbon dioxide and give off oxygen during photosynthesis.
Plant leaves allow gas exchange between air spaces in the spongy mesophyll and the exterior by opening their stomata.
When plants use food they’ve gotten, the cells respire, taking in oxygen and giving off carbon dioxide.

42. Homeostasis
Plants maintain homeostasis by keeping their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of water.
Guard cells regulate the movement of gases into and out of leaf tissues.
Stomata is opened in the daytime but closed at night.
Guard cells respond to conditions in the environment to help maintain homeostasis within a leaf.

43. Transpiration and Wilting
Osmotic pressure keeps a plant’s leaves and stems rigid.
High transpiration rate scan lead to wilting.
Wilting results from loss of water in a plant’s cells.
When a leaf wilts, its stomata closes.

44. Transport in Plants
Section 23.5

45. Water Transport
What are the major forces that transport water in a plant?
Active transport and root pressure cause water to move from soil into plant roots.
The pressure created by water entering the tissues of a root can push water upward into a plant stem.
The pressure does not exert nearly enough force to lift water up into trees.

46. Transpiration
The major force in water transport is provided by the evaporation of water from leaves during transpiration.
Transpirational pull is important because it helps a plant or tree receive water during a hot day.
The hotter the day, the more water is lost.
Also, the windier the day, the more water is lost from a plant or tree as well.

47. How Cell Walls pull water Upward
Adhesion is the attraction between unlike molecules.
Water cohesion helps make adhesion.
Water cohesion is especially strong because of the tendency of water molecules to form hydrogen bonds with each other.
The tendency of water to rise in a thin tube is called capillary action.

48. Putting it all Together
The combination of transpiration and capillary action are the major forces that move water through the xylem tissues of a plant.
Xylem tissue is composed of tracheids and vessel elements that form many hollow, connected tubes.
The tubes are lined with cellulose cell walls, to which water adheres very strongly.
When transpiration removes some water from the exposed walls, strong adhesion forces pull in water from the wet interior of the leaf.

49. Nutrient Transport
What drives the movement of fluid through phloem tissue in a plant?
The leading explanation of phloem transport is called pressure-flow hypothesis.
First, active transport moves sugars into the sieve tube from surrounding tissues.
Second, water then follows by osmosis, creating pressure in the tube at the source of the sugars.
Third, if another region of the plant has a need for sugars, they are actively pumped out of the tube and into the surrounding tissues.
Changes in nutrient concentration drive the movement of fluid through phloem tissue in directions that meet the nutritional needs of the plant.