Life Sciences, Part 16

Question 1: Define and describe the following structures that are unique to plant cells: cell wall, chloroplast, plastid, and plasmodesmata.

Answer 1: Cell wall: Made of cellulose and composed of numerous layers, the cell wall provides plants with a sturdy barrier that can hold fluid within the cell. The cell wall surrounds the cell membrane.Chloroplast: This is a specialized organelle that plant cells use for photosynthesis, which is the process plants use to create food energy from sunlight. Chloroplasts contain chlorophyll, which has a green color. Plastid: This is a membrane-bound organelle found in plant cells that is used to make chemical compounds and store food. It can also contain pigments used during photosynthesis. Plastids can develop into more specialized structures such as chloroplasts, chromoplasts (make and hold yellow and orange pigments), amyloplasts (store starch), and leucoplasts (lack pigments, but can become differentiated).Plasmodesmata (sing. plasmodesma): These are channels between the cell walls of plant cells that allow for transport between cells.

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Question 2: Compare eukaryotic and prokaryotic cells.

Answer 2: The main difference between eukaryotic and prokaryotic cells is that eukaryotic cells have a nucleus and prokaryotic cells do not. Eukaryotic cells are considered more complex, while prokaryotic cells are smaller and simpler. Eukaryotic cells have membrane-bound organelles that perform various functions and contribute to the complexity of these types of cells. Prokaryotic cells do not contain membrane-bound organelles. In prokaryotic cells, the genetic material (DNA) is not contained within a membrane-bound nucleus. Instead, it aggregates in the cytoplasm in a nucleoid. In eukaryotic cells, DNA is mostly contained in chromosomes in the nucleus, although there is some DNA in mitochondria and chloroplasts. Prokaryotic cells usually divide by binary fission and are haploid. Eukaryotic cells divide by mitosis and are diploid. Prokaryotic structures include plasmids, ribosomes, cytoplasm, a cytoskeleton, granules of nutritional substances, a plasma membrane, flagella, and a few others. They are single-celled organisms. Bacteria are prokaryotic cells.

Question 3: List four functions of mitochondria and some facts about this organelle.

Answer 3: Four functions of mitochondria are: the production of cell energy, cell signaling (how communications are carried out within a cell, cellular differentiation (the process whereby a non-differentiated cell becomes transformed into a cell with a more specialized purpose), and cell cycle and growth regulation (the process whereby the cell gets ready to reproduce and reproduces). Mitochondria are numerous in eukaryotic cells. There may be hundreds or even thousands of mitochondria in a single cell. Mitochondria can be involved in many functions, their main one being supplying the cell with energy. Mitochondria consist of an inner and outer membrane. The inner membrane encloses the matrix, which contains the mitochondrial DNA (mtDNA) and ribosomes. Between the inner and outer membranes are folds (cristae). Chemical reactions occur here that release energy, control water levels in cells, and recycle and create proteins and fats. Aerobic respiration also occurs in the mitochondria.

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