Plants cells are complex structures with several organelles lacking in animal cells. This unit will explore these structure at the macroscopic and microscopic level.
- 9: Cells and Tissues
- A cell is the smallest unit of a living thing. Organisms can be unicellular or multicellular. Thus, cells are the basic building blocks of all organisms. Several plant cells of one kind that interconnect with each other and perform a shared function form tissues.
- 10: Roots
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- Roots are an important plant organ. They anchor the plant, transport water, minerals, and sugars, and store excess nutrients.
- 11: Stems
- The stem is an organ of the shoot system that functions in support, conduction, photosynthesis, and storage.
- 12: Leaves
- Leaves are the organs of the shoot system adapted for photosynthesis. They often consist of a petiole and a blade. Leaves differ with respect to their arrangement on the venation, and shape. Internally, leaves consist of three main tissues: epidermis, mesophyll, and vascular bundles. Some leaves are modified for other functions such as defense, storage, or attachment.
Thumbnail Image: Cross section of a beach grass leaf from Berkshire Community College Bioscience Image Library (public domain).
Unit 2: Plant Structure - Biology
Cells conduct long distance signaling through the use of hormones and short distance signaling in two different ways. The two kinds of short distance signals are paracrine and synaptic signals. Paracrine signaling involves the use of local regulators. Local regulators are substances (compounds) that influence cellular activities. Local regulators are secreted by one cell in all directions. They then stimulate the "receiver" cells, who respond to contact with the local regulators and proceed to carry out a certain activity dictated by the regulator. Synaptic signaling occurs within a animals nervous system. A nerve cell sends what is known as a neurotransmitter to a targeted cell. The distance from the original cell to the target cell is so small that the cells are nearly touching. This space is called the synapse. Because of the synapse, the secreted neurotransmitters interact with only one target cell. Once the transmitter is received the target cell sends the transmitter to another cell, thus the signal is able to travel any where it needs to go without triggering unneeded responses from other cells. Synaptic signaling is a very specific local signal. Both of these signals are local because they interact with cells directly near them.
Hormonal signaling is used for long distance signaling. In hormonal signaling, cells send hormones into the circulatory system of the animal. Once there, the hormones are carried throughout the body to their destination. They are delivered at the destination and attach as ligands to the protein receptors on the outer plasma membrane of other cells. Plant cells also use hormones for cell signaling, however, while some hormones travel in vessels, other hormones simply diffuse through the plant cells.
This question relates to the main idea of, " Biological systems utilize energy and molecular building blocks to grow, reproduce and maintain homeostasis." Cell to cell signaling triggers responses from target cells. these responses create changes in cells that help maintain homeostasis within an organism. With out signaling, cells would not carry out the functions they would need to do and a organism would not be able to function properly. The molecular building blocks in this case are ligands. The ligands help maintain homeostasis within an organism by triggering needed responses from target cells. That is how the question and big idea relate.
9.1.4 Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils.
Bulbs: These are modified leaf bases which serve as food storage and thereby enable the plant to survive adverse conditions.These leaf bases may look like scales or they may extend over and encircle the centre of the bulb (onion). At the base of the bulb, a modified stem can be seen. Roots grow from the underside of the base while the new stems and leaves arise from the upper side of the base. An example of a bulb is an onion bulb.
Stem Tubers: These are modified stems which serve as food storage. The stem extends into the ground and forms enlarged, swollen structures which we call stem tubers. Stem tubers are used to store nutrients and therefore allow the plant to survive winter as well as other adverse conditions. They also serve as a mean of asexual reproduction as new plants develop from these stem tubers. An example of a stem tuber is a potato.
Figure 9.1.4 - Potato tubers
Storage Roots: These are modified roots which serve as food storage. They also allow the plant to survive adverse conditions. An example of a storage root is a carrot.
Figure 9.1.5 - Carrot storage root
Tendrils: These are modified leaves. They are slim and provide attachment as well as support. In doing so they allow plants to climb upwards. They will rotate in the air until they reach a solid structure to which they can attach to. An example of plants with tendrils are grape vines.
Figure 9.1.6 - Grape vine tendrils