Plants

1. Plants

2. Anatomy of Plants • The anatomy of a plant in its most simplistic form can be divided into the roots and the shoots • Roots are portions of the plant that are below the ground • Shoots are the portion of the plants that are above the ground • The roots work their way through the terrain, working as an anchor to keep the plants in place. • In addition, the roots work as gatherers, absorbing the water and nutrients vital to a plants survival

3. Tissue System • There are three plant tissue systems to know: • Ground • Vascular • dermal

4. Ground Tissue • The ground tissue, that makes up most of the body of the plant, is found between the dermal and vascular systems and is subdivided into three cell types: • Collenchyma cells • Parenchyma cells • Sclerenchyma cells

5. Collenchyma Cells • Live cells that provide flexible and mechanical support • Often found in stems and leaves

6. Parenchyma Cells • The most prominent of the three types, with many functions • When found in leaves are called mesophyll cells • Allow CO2 and O2 to diffuse through intercellular spaces • (owing to the presence of large vacuoles, these cells play a role in storage and secretion for plants

7. Sclerenchyma Cells • Protect seeds and support the plant

8. Vascular Tissue • Plant vascular tissue comes up often on the AP exam. There are two characters you need to be familiar with… can you guess what they are?

9. Xylem • This structure has multiple functions • It is a support structure that strengthens the plant • Functions as a passageway for the transport of water and minerals from the soil Sad fact:  most xylem cells are dead

10. Xylem • Xylem can be divided into two categories: • Vessel elements and tracheid cells • They both function in the passage of water, but vessel elements move water more efficiently because of structural differences

11. Phloem • This structure also functions as a “highway” for plants • Assisting in the movement of sugars from one place to another

12. Phloem • Unlike the xylem, the functionally mature cells of a phloem, sieve-tub elements, are alive and well

13. Hmmmmm….? • What are some ways you can remember the differences between the xylem and phloem???? I wonder who is sooooo smart?

14. Dermal Tissue • Dermal tissue provides the protective outer coating for plants • It is the skin, or epidermis • This coating attempts to keep the bad guys (infectious agents) out, and the good guys (water and nutrients) in

15. Dermal Tissue • Within the epidermis are called guard cells • What do you think they do? • They control the opening and closing of gaps called stomata that are vital to the process of photosynthesis

16. Photosynthesis.. What’s that?!? • What is the formula for photosynthesis? • + +  + + • Who can summarize the process of photosynthesis?

17. Roots • How do plants get their nutrients? • Through the hard work of roots, whose tips absorb nourishment for the plant (minerals and water) via root hairs

18. Roots • Most of the water and minerals are absorbed by plants at the root tips, which have root hairs extending from their surface • These hairs create a larger surface area for absorption

19. Roots • A root is not just a root, for not all root structures are the same • There are two types of angiosperm plants- dicots and monocots • Dicots are known for having a taproot system • Monocots are associated with fibrous roots

20. Taproot System • The taproot system (e.g. carrot) branches in a way similar to the human lungs; • The roots start as on thick root on entrance to the ground • then divide into smaller and smaller branches called lateral roots underneath the surface which serve to hold the plant in place

21. Fibrous Roots • These roots provide plants with a very strong anchor in the ground without going very deep into the soil What type of environments would these roots be helpful??

22. Root System Summary • Dicots  taproot  thick entry root  division into smaller branches • Monocots  fibrous roots  shallow entry into ground  strong anchor effect

23. Root Structure • Lets take a look at the structure of a root moving from outside to inside • The root is lined by the epidermis • Cells that give rise to root hairs (that plants must thank for their ability to absorb water and nutrients)

24. Root Structure • Moving further in, we come to the cortex, • the majority of the root that functions as a starch storage receptacle • Why would plants need starch? What type of organic compound does it fall under?

25. Root Structure • The inner most layer of the cortex is composed of a cylinder of cells known as the endodermis • These cells are important to the plant because walls between these cells create an obstacle known as the, casparian strip, which blocks water from passing • This is one of the mechanisms by which plants control the flow of water

26. Root Structure • Moving in through the endodermis, we come to the vascular cylinder, which is composed of a collection of cells known as the pericycle • The lateral roots of the plant are made from the pericycleand hold the vascular tissue of the root

27. Root Growth • Plants grow as long as they are alive as a result of the presence of meristemic cells • Early on in the life of a plant, after a seed matures, it sits and waits until the time is right for germination

28. Root Growth • At the point of germination, water is absorbed by the embryo, which begins to grow again • When large enough, it busts through the seed coat, beginning the journey into plant-hood

29. Root Growth • At the start of the journey, the growth is concentrated in the actively dividing cells of the apical meristem • Growth in this region leads to an increase in the length of a plant: primary plant growth

30. Root Growth • Later on growth occurs in cells known as the lateral meristems, which extend all the way through the plant • This growth that leads to an increase in the width of a plant and is known as secondary plant growth

31. Regions of Growth • Root cap: protective structure that keeps roots from being damaged during push through soil • Zone of cell division: section of root where cells are actively dividing • Zone of elongation: next section up along the root, where cells absorb H2O and increase in length to make the plant longer • Zone of maturation: section of root past the zone of elongation where the cells differentiate to their finalized form (phloem, xylem, parenchyma, epidermal, etc).

32. Plants Concept Check 1- Roots and Shoots • Which structure acts as a passageway for the transport of minerals and water from the soil and a support structure? • What are the gaps underneath the leaves called that are vital to the process of photosynthesis? • What structure is responsible for controlling the flow of water? • What is responsible for making the lateral roots? • Describe in 5 sentences or MORE the process of photosynthesis.

33. The Shoot System • Now that we have discussed roots- the parts of plants that are in the ground- lets take a look at the shoots (leaves and stems) the parts of the plant that are out of the ground

34. Structure of a Leaf • Leaves are protected by the waxy cuticle of the epidermis, which functions to decrease the transpiration rate. • What’s that? • Inside the epidermis lies the ground tissue of the leaf, the mesophyll, which is involved in the ever-so-important process of photosynthesis.

35. Structure of a Leaf • There are two important layers to the mesophyll • The palisade mesophyll- where most of the photosynthesis of the leaf occurs, where there are MANY chloroplasts • The spongy mesophyll- a bit farther in where cells provide CO2 to the cells performing photosynthesis

36. Structures of a Leaf • Stomata are important structures to successful photosynthesis • Controlled by guard cells that line the walls of the epidermis

37. Structures of a Leaf • Extending a bit further inside the leaf, we find the xylem • What does the xylem bring? • And the phloem • What does the phloem do?

38. Structures of a Leaf • In C4 plants, a second type of cell called a bundle sheath cell surrounds the vascular tissue to make the use of CO2 more efficient and allow the stomata to remain closed during the hot day time hours, • These cells prevent excessive transpiration

39. Structure of Stems • Again, lets travel from the outside in and discuss the basic structure • The epidermis of the stem provides protection and is covered by cutin, a waxy protective coat • The cortex of a stem contains parenchyma, collenchyma, and schlerenchyma cells. • What are the characteristics of each of these cells?

40. Structure of Stems • You’ll notice that there is no endodermis in the stem • This is because this portion of the plant is not involved in the absorption of water • As a result, the next structure moving inward is the vascular cylinder and once again the xylem and phloem

41. Structure of Stems • A term to know is the vascular cambium • It extends along the entire length of the plant and gives rise to secondary xylem and phloem • Over time, the stem of a plant will increase in width because of the secondary xylem produced each year

42. Structure of Stems • Another term to know is the cork cambium- • Produces a thick cover for stems and roots • This covering replaces the epidermis when it dries up and falls off the stem during secondary growth, forming a protective barrier against infection and physical damage

43. Structure of Stems • The growth of plants is not a continuous process in seasonal environments • There are periods of dormancy in between phases of growth

44. Structures of Stems • Rings of a stem • These rings produced each year are a window into the past, and give insight into the amount of rain a tree has encountered in a given year • The wider the ring, the more water is saw

45. Plant Hormones • Hormones perform the same general function for plants that they do for humans • They are signals that can travel long distances to affect the actions of another cell • There are 5 main plant hormones you will need to know; abscisic acid, auxin, cytokinins, ethylene, gibberellins

46. Plant Hormones • Abscisic Acid • The “babysitter” hormone • It makes sure that seeds do not germinate too early, inhibits cell growth, and stimulates the closing of the stomata to make sure that the plant maintains enough water

47. Plant Hormones • Auxin • A hormone that performs several functions • Leads to the elongation of stems • Plays a role in phototrophismand gravitropism

48. Plant Hormones • Cytokinins • Hormones that promote cell division and leaf enlargement • Seem to slow down the aging of leaves • Supermarkets use synthetic cytokinins to keep their veggies fresh

49. Plant Hormones • Ethylene • This hormone initiates fruit ripening • Causes flowers and leaves to drop from trees (associated with aging)

50. Plant Hormones • Gibberellins • A hormone group that assists in stem elongation • When you think gibberellins, think “grow” • It induces the growth of dormant seeds, buds, and flowers