Hibiscus

Above is a hibiscus flower similar to the one we dissected today. Remember how we wondered about the unusual anther and stamen modification where the anthers seem to be on the side of the pistil and the stigma is modified so that there are five stigma pads in all?

The Pistil

The ovary of the hibiscus is found within the petals rather than below them. Each hibiscus ovary has five ovule chambers and can produce five seeds. At the top of its style, the hibiscus has a modified stigma consisting of five branches with a stigma pad on top of each.

The Stamens

The male reproductive structure in a plant is called the stamen. It is made up of the anther that holds the pollen and a stalk called the filament on which the anther sits. In a hibiscus flower, the filaments fuse into a tube that surrounds the style. Numerous, brightly coloured anthers stick out from the fine filaments almost like the feathers with the stigma pads located above the anthers.

Be sure to visit the website below to see incredible magnified images of the parts of a hibiscus flower:

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artfeb07/bj-Hibiscus.html

Leaf Abcission

Fall is here at last and it is getting harder and harder to get up early! The days are shorter and the nights are longer and a little chillier and it is nearly time to dust down those winter woollies and boots. The leaves are so beautiful in autumn, or fall as Americans say, but the science behind autumn is equally magnificent!

Now that we have studied the different pigments that are found in leaves that give autumn leaves their special colors, how about this leafy info: Did you know that the leaves do not simply fall off trees in the fall and the wind does not blow them off either? Nope. The story is way cooler than that. Trees actually activate abcission cells or scissor cells that make a nice neat cut at the base of the petiole and then the leaves falls off because they are told to do so!

Follow the link to read more about this incredible phenomenon:

Scissor cells in plants in the fall

Look at the diagram above carefully and you will see the abcission or scissor cells have been stained red for easy identification. The leaf is to the left and the stem to the right of the abcission cells.

Above you will see that the when the leaf falls off, the tree is left with a typical leaf scar. The dots in the leaf scar are left by the xylem and phloem vessels in the vascular bundle that runs from the leaf to the rest of the tree which is why that part of the leaf scar is called the bundle scar.

Look what I found below in the garden! The kale plants are making plans for winter as we speak. It looks like scissor cell activity to me..

 

 

Chloroplast Structure

Image: (http://www.printablediagram.com/)

Take a good look at the stack of thylakoids called a granum. When you see the word thylakoid a green light should come on in your brain as you remember that this is where the chlorophyll is found and this is where the light reaction of photosynthesis takes place.

Why is chlorophyll green anyway? Chlorophyll appears green to our eyes because most of the light it absorbs is blue and red, leaving behind the rest of the color spectrum, which averages out to green.

The reason chlorophyll absorbs blue and red light is because these very specific energy wavelengths are used to break the bonds in the molecules involved in photosynthesis.

Stomata

Well hi there everyone. We are travelling to the underside of a leaf and by now you know that you are looking at the lower epidermis and the surface where veins are most prominent. At a cellular level we also find stomata or openings on this surface of leaves although water plants like waterlilies also have stomata on the upper surface of the leaf.

In the images above you can clearly see stomata that are either open or closed at various magnifications. The opening and closing of stomata is essential for plant survival and is a highly regulated process dependant on a high level of cell specialization.

In the diagram above you can see that each stoma has two guard cells that control the opening and closing of the pore. When the stoma is open, there is an accumulation of potassium ions (salt) in the guard cell and water flows into the guard cells and the vacuoles fill up and pull the pore open.  When the guard cells lose water the vacuoles shrink and the pore closes. There are four factors that are affecting the opening and the closing of the stomata:

1. light: stomata are usually open during the day allowing CO2 to enter for photosynthesis and O2 to leave as a product of photosynthesis.
2. water: the stoma closes when plants loose too much water and it will open when plants get enough water.
3. temperature: the stoma will open when the temperature increases.
4. mineral elements: potassium, nitrogen and phosphorus influence the opening and closing of stomata.

In the diagram above you will see that plants actually take in O2 at night and release CO2. During the day plants use light energy to produce sugars, carbohydrates and O2. At night plants burn the products of photosynthesis made during the day by respiration to stay alive. They need O2 from the atmosphere for this to occur and release CO2 into the atmosphere just like humans and animals.

The discoveries of Christian Konrad Sprengel

Christian Konrad Spengel, a German naturalist made several important botanical observations and discoveries. He published his studies and theories in the book seen below in 1793. Notice the incredible detail in his drawings. One thing is certain. He must have done lot of observation!

Leaf cross section

Image from https://rbf-productions-nl.deviantart.com/art/leaf-cross-section-model-200809405

Above is a wonderful Play-Doh model of the cross section of a leaf. Kinda weird to think that all of this goes on inside a leaf that is about as thin as thin card when you look at it with the naked eye.

Above you can see a leaf cross section as seen under a microscope. See if you can spot the structures seen in the Play-Doh model. Notice how there are air spaces inside the leaf between the cells. These gaps are filled with gas that the plant uses (carbon dioxide – CO₂ ) and gases that the plant is expelling (oxygen – O₂, and water vapor).  Here is some great additional info on the function of the different layers of cells in a leaf: Leaf cell layer structure and function

Image from https://www.purposegames.com/game/e974e48249

Take a look at the vascular tissue in the leaf tissue anatomy illustration above. Notice the vascular tissue containing the xylem and phloem. What you are looking at is a section through a leaf showing part of the leaf vein. The vein consists of two types of vascular tissue that transport water and the products of photosynthesis. Xylem is normally on the upper side of the leaf vein and phloem vessels are on the bottom.

Look carefully at the microscope images above of a cross section through a leaf and you will clearly see the vein cross section with the vascular bundle containing xylem and phloem vessels (red) as well as air spaces between cells and the different layers of cells that make up a leaf.