Biology 101, Chapter 2, The 3rd Day - Plants

In addition to Biology 101:
• Grow a bean plant, learn about tropisms
• Dissect a Flower (worksheets here or here)
• Apologia Biology Exp. 14.1 - Leaf Collection and Identification (worksheet, guide)
• Apologia General Science Exp. 10.4 - Turgor Pressure (scroll down) (directions/worksheet)
• Transpiration - Apologia Botany p. 96 or 138.  Place a baggie over a leaf of a well-watered plant that is in the sun.  Close baggie with clothespin or twist-tie.


(1) Plant Cells


All cells have a cell membrane.  But outside a plant's cell membrane, there is also a cell wall.  
The cell wall of plants is made of cellulose.  
There are three structures in a plant cell that pertain specifically to plant cells.

1. cell wall (for stiffness of the stem; also keeps cell from bursting if the central vacuole continued to fill)
2. large central vacuole (for turgor pressure)
3. chloroplasts (for photosynthesis)

(2) Turgor Pressure
The large central vacuole and the cell wall work together to create turgor pressure.
As the water vacuole fills, it presses against the cell wall, making the plant become more rigid.  This rigidness is known as turgor pressure.
This plant regains turgor pressure as the vacuoles in each of its plant cells fill with water.
(459 shots, made every 30 seconds for 3h 45m. He added about 1½ cups of water.)



The food coloring in the water shows that the water traveled up the xylem, filled the celery's plant cell vacuoles, and caused the plant to become rigid with turgor pressure.

(3) Plant Parts


►But what about a daisy?  Where is the stigma?  Where is the stamen?
Read this article (scroll to Inflorescence and then The Magic.)
Then look at these microscopic images.



(4) Leaves
►See several labeled images of leaves here.

►A great site that classifies leaves.  (Also see the paragraph about bark)
• Scroll down and see what kinds of fruits there are, including nuts.
• These are important to think about when classifying leaves in class.

These links will help with leaf identification.
► Keys to Leaves of Virginia, (4H) I've got my leaf; let's get started! (interactive)
► Auburn University Horticulture Dept, Plant Identification Resource (interactive)

The microscopic structure is what you cannot see with the naked eye.

►Image of what is inside a leaf (scroll down)

Structure of a Leaf



Parts of a Leaf




(5) Stems
Xylem and Phloem  (zy' lum, flow' um)
♦Xylem and phloem tubes are together in a vein, or a vascular bundle.
If you look at the bottom of a stalk of celery, you will see these.  They look like strings, and both xylem and phloem are bundled together, like wires through a power cord.
♦ The xylem transports water and minerals UP the roots to the leaves where the chlorophyll is located, in order to make food for the plant.
Xylem is dead tissue.
♦ The phloem transports food (sugars) back DOWN the leaves, then to all the rest of the parts of the plant.



(6) Transpiration - how water and minerals are transported up the xylem (which is dead tissue) and how moisture exits the leaves through the stoma so that more water and minerals are pulled up through the xylem.
 stoma/stomata, guard cells, vacuoles


►Remember that plants have specialized structures while algae do not.  In other words, plants have structures that each perform their own specific task.
(1) Roots take in water and minerals.
(2) The stem transports these to the leaves.
(3) The leaves carry out photosynthesis.



(7) Tropisms

Stimulus:  something causing a response.

Nastic Movement vs. Tropism

►Nastic movement is a preprogrammed response, and any direction of movement is independent of the direction from which the stimulus comes.  No matter from which direction the light comes, the plant's response is the same each morning -- opening of leaves and petals.  Or if a plant's leaves close when you touch them, it does not matter which direction the touch is from.  The plant is preprogrammed to this action.
Nastic movement is not a growth response.
It does not grow in a direction as a result of a stimulus.

►Tropisms depend on the direction of the stimulus, and therefore, can change.
Tropisms can be a growth response or a movement response.
• Growth of a plant toward sunlight is phototropism.  The sunlight is the stimulus.
• Heliotropism is when plants bend toward the sun as it moves across the sky.  This is a movement response that is a tropic response since it depends on the direction of the stimulus.
--These are tropisms if the plant moves or grows toward the light, rather than just opening its leaves as in nastic movement.   
• Thigmotropism is a growth response to touch, like a vine touching a branch will grow around the branch.  The direction of growth depends on the direction of the branch.  The branch is the stimulus.
Tropisms are growth or movement responses, but both depend on the direction of the stimulus.
• Gravitropism (also called geotropism) works in two ways.  Roots grow down, and shoots grow up.  The shoots growing up is not simply a result of phototropism, because they will grow up even in the dark.  The seeds that germinate and sprout upwards while still covered with soil are proof of this.  This is called negative gravitropism, since they grow in the opposite direction of gravity.  Roots growing down is positive gravitropism.
• Hydrotropism is growth toward water.  This would most likely be roots growing toward water.

(7a) Examples of nastic movement (not a growth response like a tropism can be)
Nastic movement because it does not matter from which direction the bug comes.
This is a preprogrammed response to happen when the hairs are touched.   


(7b)More nastic movement
Nastic movement because it does not matter from which direction the leaves are touched.   
This is a preprogrammed response to happen when touched.    


(7c)Nastic movement of a Moon Flower, also called an Evening Primrose
It opens near dusk and it takes about 30 to 60 seconds for one to open. About 10 to 20 open each night on a plant and they all fade by noon the next day.
♦ This is in real time, not a time lapse.
Nastic movement because there is nothing in any direction that prompts this behavior.  
This is a preprogrammed response for this to happen at night. 

LOL, dh asked about pollination, and I told him they're open until noon the next day.
He laughed and said they only serve breakfast.  =)


Tropisms can be a movement OR a growth response.
(7d) Phototropism, and a little about gravitropism 
These are growth responses as a result of the direction of the stimulus - the sun, or gravity.

(7e) Phototropism and Heliotropism

Watch these bush beans as they grow toward the sun. (phototropism)
Then watch as shadows move over them - they ALL lean toward the sun. (heliotropism)
(Video was shot over a 24 hour period.)
Growth and Movement response is a result of the direction of the stimulus - the sun.


(7f) Thigmotropism - response to touch (what the plant touches, not what touches the plant - like a human or animal)
Growth response as a result of the direction of the stimulus - the pole.  The vine would not grow this direction if it were not for the pole.
LOL at the spider that comes down at 0:12  =D