Roots, Stems & Leaves

1. Roots, Stems & Leaves Chapter 23

2. Overview of the Cell

3. Nucleus • The nucleus contains nearly all of the cell’s DNA, which includes all the instructions for making proteins and other important molecules. Also contains a structure called the nucleolus, where ribosomes are produced.

4. Cell Membrane • The cell membrane (or plasma membrane) regulates what enters and leaves the cell, and provides protection and support. Many substances can pass through the cell membrane, through active or passive transport.

5. Cell Wall • The cell wall (found in plants, algae, and fungi, but not in animals) lies outside the cell membrane. The main function of the cell wall is to provide support and protection for the cell. Plant cell walls are made mostly of cellulose. Most cell walls are porous enough to allow transport of some materials in and out of the cell.

6. Cell Wall

7. Cytoplasm • The portion of the cell outside the nucleus is the cytoplasm or plasma. The cytoplasm includes all of the specialized structures that carry out specific tasks within the cell. These structures are known as organelles. • The main organelles are:

8. Ribosomes • Ribosomes are small particles of RNA and protein where the coded messages from DNA are used to produce proteins.

9. Endoplasmic Reticulum (ER) • The ER is an internal membrane system where lipid components of the cell membrane are assembled. • Some ER is covered in ribosomes, and the proteins produced by those ribosomes are moved into the ER to be modified. This type of ER is known as rough ER because of its appearance. • Other portions of the ER do not have ribosomes, and is known as smooth ER. This smooth ER often contains specialized enzymes to perform specific tasks.

10. Rough & Smooth ER

11. Golgi Apparatus • The Golgi apparatus functions to modify, sort, and package proteins and other materials from the ER, for storage in the cell or export from the cell.

12. Lysosomes • These are small organelles filled with enzymes, they are designed to digest or breakdown lipids, carbohydrates, and proteins into small molecules that can be reused by the cell. • Lysosomes perform the vital function of cleaning up “junk” in the cell, including breaking down old organelles and other items that would clutter up the cell.

13. Vacuoles • These are saclike structures that store materials such as water, salts, proteins, and carbohydrates. • Plant cells often contain a central vacuole filled with liquid. This central vacuole helps to maintain the structure of the plant through turgor pressure.

14. Central Vacuole

15. Mitochondria • These are organelles that convert stored chemical energy from food into compounds that can be use immediately by the cell for energy. • Mitochondria are known as the “powerhouse” of the cell.

16. Chloroplasts • Chloroplasts – these are organelles that capture the energy from sunlight and convert it into chemical energy through photosynthesis.

17. Label Your Diagram

18. Label Your Diagram

19. Colour-Code your Diagrams • Pick a colour for each type of organelle or structure, use it to underline the term in your notes and on the diagram • Then colour in that structure in that colour • If the structure is found in both types of cells, then use the same colour for both! • This diagram will go into your logbook • I’ll play a couple of summary videos while you colour 

20. Crash Course - Cells • Eukaryotic cells (animal cells) https://www.youtube.com/watch?v=cj8dDTHGJBY (11:34) • Plant cells • https://www.youtube.com/watch?v=9UvlqAVCoqY (10:30)

21. Seed Plant Structures • Roots – Roots absorb water and dissolved nutrients and transport them to the rest of the plant. Roots also anchor the plant in the soil and hold plants upright against wind and rain. • Stems – Stems include a support system, a transport system, and a defense system. • Leaves – Leaves are the main site of photosynthesis – the broad surfaces allow for effective light absorption, but also make water loss an issue, so leaves also need to contain systems to reduce water loss.

22. Plant Tissue Systems • Plants contain 3 main tissue systems – Dermal tissue, vascular tissue, and ground tissue.

23. Dermal Tissue • Dermal tissue is like the skin of a plant, it consists of a single layer of cells called epidermal cells. These cells are often covered in a waxy coating (the cuticle) to protect against damage and prevent water loss.

24. Dermal Tissue • Dermal cells sometimes have tiny projections called trichomes, which protect the leaf (this is also why leaves sometimes look fuzzy). • On the bottom of leaves, the dermal tissue includes guard cells to regulate water loss and gas exchange through the stomata. • In roots the dermal cells include root hairs which increase the surface area for water absorption.

25. Vascular Tissue • Vascular tissue makes up a transport system to move water and nutrients throughout the plant. • The main subsystems are the xylem (water-conducting tissue) and phloem (food-conducting system). • Both these systems are made up of systems of hollow, specialized cells that can carry fluids through the plant body.

26. Xylem • Xylem is made up mostly of cells called tracheids; long narrow cells with cells walls that are impermeable to water. There are openings in the cell walls to connect neighbouring cells together. • These cells mature and die, and their cytoplasm disintegrates, leaving a series of hollow cells that are interconnected.

27. Vessel Elements • Angiosperms have an additional type of xylem cell, called a vessel element. • They also mature and die, leaving hollow cells behind, but they are much wider than tracheids, and the cell walls at their ends are lost when the cell dies, creating a continuous tube, through which water can flow easily.

29. Phloem • Phloem is made up mostly of cells called sieve tube elements. These cells are placed end to end, like vessel elements, to form sieve tubes. • The end walls have many small holes in them. As sieve tube elements mature, they lose their nuclei and most other organelles. Any remaining organelles stick to the side walls. • The cell is then mostly cytoplasm, and sugars and other substances can be easily transported from one cell to another through the holes in the end walls.

30. Phloem – Companion Cells • Phloem also contains companion cells, which surround sieve tube elements. These cells keep their nuclei and other organelles, and they support the phloem cells and help to move substances into and out of the phloem.

31. Ground Tissue • All the cells between the dermal tissue and the vascular tissues are known as ground tissue. In most plants, the main cells in the ground tissue are parenchyma cells.

32. Parenchyma Cells • These cells have thin cell walls, large central vacuoles and a thin layer of cytoplasm. In leaves these cells are packed with chloroplasts, and are the site where most photosynthesis takes place.

33. Ground Tissue • There are 2 other types of cells found in ground tissue, both with thicker cell walls. • Collenchyma cells have strong, flexible cell walls that help to support larger plants. • Sclerenchyma cells have extremely thick and rigid cell walls to make the ground tissue tough and strong.

34. Plant Growth & MeristematicTissue • Plants produce new cells at the tips of their roots and stems for as long as they live. These new cells are produced at meristems – clusters of tissue that produce new cells through mitosis. A meristem that is found at the tip of each growing root or stem is called an apical meristem.

35. Meristems • The new cells produced by the meristems are initially undifferentiated (not yet specialized). As they mature, they take on specialized structures and functions to become part of particular tissue-types. This process is called differentiation.

36. Floral Meristems • In angiosperms, certain shoot apical meristems can have particular genes turned on, and they change into floral meristems. A floral meristem produces both the modified leaves that become the petals, and the reproductive tissues of the flower.

37. Celery Demonstration • I’ll set it up, fill in your predictions • We’ll fill in the “before” masses • We’ll check it again next week to see what has happened.

38. Roots • When a new seed germinates, it produces its first root to absorb water and nutrients from the soil, then other roots branch out from the first to increase the surface area. The total surface area of the roots can be much larger than that of the stems and leaves.

39. Types of Roots • There are two main types of roots • Taproots – found mostly in dicots • The primary root grows long and thick, any secondary roots remain small • Some tap roots of trees can grow long enough to reach water in aquifers • Examples: carrots, dandelions, beets, radishes

40. Types of Roots • Fibrous roots – found mostly in monocots • No single root grows larger than the others, there is extensive branching • These roots help to prevent topsoil from washing away in heavy rain • Examples: grasses, coconut palm

41. Types of Roots

42. Root Structure • Roots contain cells form all three tissue layers: dermal, vascular, and ground tissue.

43. Dermal System • The epidermal system of the root has two functions, protection & absorption • Covered in cellular projections called root hairs • Penetrate the spaces between soil particles and increase the surface area for water absorption • There’s also an endodermal layer between the ground tissue and the vascular tissue • Completely surrounds the vascular cylinder

44. Ground Tissue • A spongy layer of ground tissue called the cortex is sandwiched between the epidermis and endodermis

45. Vascular Tissue • The vascular cylinder of xylem and phloem allows water, nutrients, and sugars to be transported into and out of the roots.

46. Root Growth • The root grows as the root apical meristem produces new cells near the root tip. Most of the increase in root length is produced at this meristem, as new undifferentiated cells elongate and then differentiate into their specialized cell types.

47. Root Growth • These new cells are fragile and would be damaged when pushing through the soil, so they must be protected by a tough root cap. The root cap also produces a slippery secretion to help the root move through the soil more easily. Cells on the root cap are continuously scraped away and must be replaced regularly.

49. Amazing Plant Roots • https://www.youtube.com/watch?v=_jVyhSe5pvk (3 min)

50. Root Functions • Water does not just “soak” into the root from the soil - the plant has to spend energy to absorb water.