1. Plant Organs and Transport
Sections 13.3 – 13.4

2. Learning Goal
To learn more about the details of plant organs and their functions
To better understand how water and nutrients move in and out of plant cells

3. Introduction – Review Parts of Plant cell

4. Roots
Root system is usually the 1st structure to grow from a seed when it sprouts
Roots have 3 Main Functions:
Take in water and dissolve minerals that are transported to where needed in the rest of the plant
Anchor the plant in the soil to support the plant against forces like wind and water
Store the carbohydrates that are produced by photosynthesis in the leaves or green stems, as well as water and other nutrients

5. Root Structure and Function
The tip of the root is covered by the Root Cap
The Root Cap is made up of parenchyma cells that help protect the growing tissues as the root extends through soil or more resistant materials, like rocks

6. Root Structure and Function
The roots apical meristem produces new cells that develop into different types of root tissues that have different functions
Example- some replace lost cells due to friction, while others grow and increase the length of the root

7. Outer Root Layers
Like the rest of the plant, the root is covered in a layer of Dermal Tissue
Epidermal cells produce root hairs that increase the surface area of the root
This increases the area where the root is able to absorb water and dissolve mineral

8. Outer Root Layers Just inside the epidermis is the Cortex
The cortex lies between the epidermis and the vascular tissue of the root
This layer is made up of ground tissue (made of parenchyma cells) that transport and store water, food, and minerals
All materials that enter the root pass through the cortex to get to the vascular tissue, to the rest of the plant

9. Outer Root Layers
On the inside edge of the cortex, between the cortex and the vascular tissue is called the layer called the Endodermis
This is one THICK cell that is surrounded by a waterproof band called a Casparian strip
Forces water and minerals to cross the plasma membrane through the cytoplasm
So that the endodermal cells control only water and certain nutrients to enter the vascular system

10. Outer Root Layers

11. Inner Root Vascular Tissue
Inside the endodermis are the vascular tissues, xylem and phloem = together they make up the Centre of the Root
The arrangement of xylem and phloem is different in monocot and dicot flowering plants

12. Types of Root Systems There are 2 main types of roots: Taproot
Fibrous Roots
Made of THICK root system with smaller lateral branching roots
Anchors plants
Absorb water and minerals
Stores food and water below ground level
Ex- Carrots , dandelions
Made up of smaller branching roots
Roots are about the same size that grow from a central point
Don’t grow as deep as taproots
Ex – grass roots, scallions

13. Types of Root Systems

14. Stems
There many different types of stems, who’s function is to provide support for the plant’s leaves and reproductive structures
Based on various adaptations, stems can be soft and flexible or hard and woody in order to help plants survive

15. Types of Stems
Stems are used to store excess food, while others help the plant withstand drought, cold, or heat
There are 5 different types of stems:
Type of Stem
Description / Example
Tuber
Like the potato – is an enlarged part of an underground stem
Bulb
Like the onion – are shortened, compress stems surrounded by fleshy leaves
Corms
Like crocuses – made up of stem tissue with some scaly leaves at its top
Stolons
Like strawberries – have horizontal stems that grow above ground along the top
Rhizomes
Like Irises – have horizontal stems that grow underground

16. Leaf Structure and Function
Regardless of the different shape or size of leaves, they all have the same function: to convert light energy from the Sun into chemical energy for food via photosynthesis

17. Leaf Structure and Function
The external structure of a typical leaf has a flat portion called the blade
The blade and the stem can attach directly or indirectly through a structure called a petiole
The epidermal cells of leaves release a waxy substance that forms the cuticle
Acts as a protective layer that keeps water in and reduce evaporation
Vascular tissue runs through the petiole, connecting the leaf, veins, and stem to transport vital nutrients throughout

18. Internal Structure of a Leaf

19. Internal Structure of a Leaf
The cuticle and the epidermis of a leaf are transparent, which lets light through it
Between the upper and lower epidermis of a leaf is the mesophyll
Right below the upper epidermis is a row of tightly packed cells celled the palisade mesophyll cells
They contain lots of chloroplast, which is why most photosynthesis takes place here

20. Internal Structure of a Leaf
Below the palisade mesophyll is the spongy mesophyll
The cells located here are irregular in shape and loosely packed to allow for gas exchange to take place, where:
Reactants CO2 + H2O move in
Waste Product O2 moves out

21. Identifying Leaves
Ventilation: the pattern
of veins in a leaf

22. Flowering Plants: Mono vs. Dicots
Flowering plants can be classified as monocots or dicots based on the number of seed leaves in their embryos, where
If they have 1 seed in their embryo = monocot
If they have 2 seeds in their embryo = dicots

24. Transportation in Plants
Section 13.4

25. Introduction
Vascular plants have a conducting system to transport fluids and nutrients from 1 part of the plant to another
Basically – a plant is a tube with its base embedded in the ground, where the base of the tube is the root system, and the leaves are at the top of the tube

26. Introduction A plant needs 2 kinds of transportation
Job One – move sugars
Sugars made in the leaves by photosynthesis must be carried to all other living cells in the plant
So WATER that carries these dissolved sugars must move up and down the tube
Cells in the Phloem do this
Job Two – move water up
Water and dissolved nutrients must be taken up by the roots and sent to cells, so water moves up the tube
Cells in the Xylem do this

27. How things move in / out
Particles move based on concentration gradients – the amount of a substance on one side versus the other
This movement is called DIFFUSION
Where substances move from a HIGH concentration to a LOW concentration

28. How things move in / out
Similarly, water also moves from a HIGH [ ] to a LOW [ ]
This more specific type of diffusion is called OSMOSIS
Diffusion and Osmosis occur naturally and allow water, sugars, and nutrients to be transported throughout the plant

29. How things move in / out
However, minerals like nitrates found in abundance in the soil are needed by the plants in small amounts
Diffusion would not work in this case
Instead plants use Active Transport to intake such minerals from a LOW concentration to a HIGH concentration

30. Transport in the Xylem
The root cells have a higher [ ] of dissolved nutrients than the surrounding soil
So water moves INTO the roots by Osmosis, where:
Water moves through the root cells or intercellular spaces within the root and enters the Xylem
The water is then transported in the Xylem up through the root into the stem
Inside the stem, water moves by Osmosis into other tissues
Most minerals from the soil move via Active Transport

31. Transport in the Xylem
As the xylem tissue carrying water and minerals enters the leaf, the conducting vessels branch into the many veins
From the end of each vein, water and minerals can diffuse into the cells of the leaf
Unfortunately, more than 90% of the water that reaches the leaf evaporates out through the stomata through a process called transpiration

32. Transport in the Xylem

33. Transport in the Xylem
Long distance transport in the Xylem is done by 2 processes: Root pressure & Transitional pull
Root Pressure – where positive pressure (pushing)work with
Transitional Pull – the negative pressure (pulling) help move water move up through the xylem

34. Transport in the Xylem Root Pressure
Recall – is the mechanism that pushes water and minerals upwards in a plant
Water entering the roots create a POSITIVE Pressure that pushes water UP
Minerals move from the soil into the xylem against their [ ] gradients by Active Transport
The now added minerals in the xylem makes MORE water move up by OSMOSIS
This process is added by the adhesion (sticking) of water molecules to the cell walls of the xylem tissue

35. Transport in the Xylem Root Pressure
In shorter plants, root pressure can be seen as water droplets on leaves called guttation
This occurs under High Humidity – where water can’t evaporate from these leaves and the rate of Transpiration is low

36. Transport in the Xylem Transpirational Pull
Looks at pulling water up AGAINST Gravity
Negative pressure (Pulling) from above is the Strongest force for long-distance heights
The COHESION-TENSION MODEL accounts for the majority of water and minerals moving from the roots all the way up in the leaves of the tallest trees
Since more than 90% of water that is absorbed from the roots is lost via Transpiration, water from the leaves creates a negative pressure that PULLS water up to replace its loss in evaporation

37. Transport in the Xylem Transpirational Pull
There are 3 Main Factors that are vital to this model:
Transpiration – the evaporation of water molecules from the shoot system, is responsible for the movement of water and dissolved minerals upward in a plant stem. Dry air, heat, and wind cause this to take place, as water exits through the stomata

38. Transport in the Xylem Transpirational Pull
Cohesion – the columns of water in the xylem have a property called cohesion, where the force of attraction between water molecules keeps them together in the xylem

39. Transport in the Xylem Transpirational Pull
Adhesion – causes the water molecules to stick to the xylem walls. Adhesion works with cohesion to keep water from separating and keeps on being pulled up in the plant

40. Transport in the Xylem

41. Movement of water

42. VIDEO:

43. Nutrient Transport in Phloem
Photosynthesis occurs in the green parts of the plant, where sugars like glucose and sucrose are made as food for the plant
Translocation is the way in which these sugars get moved throughout the plant to areas that are needed through the phloem

44. Translocation: Pressure Flow Model
Translocation in the phloem moves sucrose from a source from any part of the plant that enter into a sieve tube (like palisade and spongy mesophyll tissues in the leaf) and into a SINK

45. Translocation: Pressure Flow Model
The SINK is any region in the plant where sugars are used or stored
For example – while flowers and fruits of a plant are developing, they are also sinks because they need organic molecules to grow
Roots are also sinks because they need nutrients to grow, and because they also store carbohydrates during the winter

46. Translocation: Pressure Flow Model
Water and minerals are mostly pulled up by translocation
Nutrients are pushed through the phloem
The Pressure-Flow Model believes plants use a combination of osmosis and pressure dynamics to explain how materials are pushed from a source to a sink via translocation
Video:

47. Translocation: Pressure Flow Model
Read pg. 564 to explain how the glass bulb analogy relates to this model

48. Translocation

49. Pressure Flow in Phloem
When nutrients are pumped into or removed from the phloem, the changes in concentration causes a movement of water in that same direction
Thus, the internal pressure builds up at the source end of the sieve tube and pushes the sucrose-rich solution toward any sink, where the sucrose is then removed

51. Pressure Flow in Phloem
RECALL:
In the xylem, it is mostly negative pressure moving water and dissolved minerals
In the phloem, its positive pressure that moves the flow of sucrose from the source into the sink

52. Pressure Flow in Phloem
The direction of flow is always from source to sink, and the sinks change depending on the plant’s stage of growth and development
Ex – in older plants, the newly synthesized leaves are a sink , and the sucrose moves there from photosynthesizing leaves to growing leaves
When fruit is forming, sucrose moves there by translocation, and growth in other areas of the plant slows down

54. Plant Transpiration LAB - http://www. mhhe