Question

1. Examine/Compare Plant and Animal Cells.

2. Identify the organelles within each type of cell and explain their corresponding function(s).

3. Describe the structure and function of cell components, with emphasis on eukaryotes.

4. Discuss the evolutionary relationship of prokaryotic and eukaryotic cells.

Answer 1

1. Differences Between Animal Cells and Plant Cells:

        Size: Animal cells are generally smaller than plant cells. Animal cells range from 10 to 30 micrometers in length, while plant cells range from 10 and 100 micrometers in length.

        Shape: Animal cells come in round or irregular shapes while plant cells are rectangular or cube shaped.

        Energy Storage: Animals cells store energy in the form of the complex carbohydrate glycogen while plant cells store energy as starch.

        Proteins: Out of 20 amino acids, only 10 are produced in animal cells and others are acquired through diet. Plants are capable of synthesizing all 20 amino acids.

        Differentiation: In animal cells, only stem cells are capable of converting to other cell types. Most plant cell types are capable of differentiation.

        Growth: Animal cells increase in size by increasing in cell numbers. Plant cells mainly increase cell size by becoming larger. They grow by absorbing more water into the central vacuole.

        Cell Wall: Animal cells do not have a cell wall but have a cell membrane. Plant cells have a cell wall composed of cellulose as well as a cell membrane.

2. organelles with their functions

Chloroplasts: In animal cells, the mitochondria produce the majority of energy from food, while plant cells use sunlight as their energy source by the process of photosynthesis. Chloroplasts are rather large, double membrane-bound structures and contain chlorophyll which absorbs sunlight. Additional membranes within the chloroplast contain the structures that actually carry out photosynthesis. The double membrane structure of chloroplasts is similar to mitochondria. The inner membrane encloses an area called the stoma, which is analogous to the matrix in mitochondria and enclose DNA, RNA, ribosomes, and different enzymes. Chloroplasts, however, contain a third membrane and are generally larger than mitochondria.

The Cell Wall: Plant cells have rigid cell wall surrounding the cell membrane. This wall can range from 0.1 to 10 micrometers thick and is composed of fats and sugars. The tough wall gives added stability and protection to the plant cell. Animal cells lack cell wall.

Vacuoles: Vacuoles are single membrane large, liquid-filled organelles found only in plant cells. It occupies up to 90% of a cell's volume. Their main function is to act as a space-filler in the cell, but they can also fill digestive functions similar to lysosomes. Vacuoles contain a number of enzymes, and act as storage for nutrients. Animal cells lack a large vacuole. They are bound by single membrane and small organelles. In many organisms vacuoles are storage organelles.

3. All eukaryotic cells contain organelles.

        a. Nucleus: Nucleus is the most prominent organelle in a cell. Eukaryotic cells have a true nucleus. The cell’s DNA is surrounded by a membrane. Nucleus houses the cell’s DNA and performs the synthesis of proteins and ribosomes.

        b. Endoplasmic reticulum (ER): The membranes of the ER are continuous with the outer nuclear membrane. ER are both rough and smooth. ER modifies proteins and synthesizes lipids, while the golgi apparatus is where the sorting, tagging, packaging, and distribution of lipids and proteins takes place.

        c. Golgi body: The Golgi body is made of several flattened membranes sacs. The number of compartments in any one Golgi apparatus is usually between 3 and 8. It modifies, sorts, and ships proteins and also play a role in the synthesis of lipids for secretion or internal use.

        d. Vesicles: a vesicle is a small structure within a cell, or extracellular, consisting of fluid enclosed by a lipid bilayer. Vesicles form naturally during the processes of secretion (exocytosis), uptake (endocytosis) and transport of materials within the cytoplasm. It transports material between organelles and function in intracellular digestion.

        e. Mitochondria: The mitochondria are a double membrane-bound organelle found in all eukaryotic organisms. These layers are composed of phospholipid bilayers and proteins. Mitochondria are commonly between 0.75 and 3 μm in diameter but vary considerably in size and structure. Mitochondrion has its own independent genome that shows substantial similarity to bacterial genomes. The main roles of mitochondria are to produce the energy of the cell, ATP by the process of respiration, and to regulate cellular metabolism.

4. Eukaryotes cells contain their genetic material in a nucleus. Eukaryotes are thought to have evolved from prokaryotes. Prokaryotes usually contain a single DNA and lack a nucleus. The early eukaryote cell might have evolved more than a billion years ago. The endosymbiosis theory states that the eukaryotic cell developed from a larger prokaryotic cell consuming smaller prokaryotic cell without digesting it. The smaller prokaryotic cell lived in the larger prokaryote, providing it with extra energy, while the larger cell protected the small bacteria, allowing it to survive. Since there are no fossil records on the evolution of eukaryotes, most of the evidence is based on the study of present-day cells. DNA analysis reveals that eukaryotes contain many bacterial genes. Mitochondria and chloroplasts inside the eukaryotic cell have single, circular DNA molecules just like bacteria.

In conclusion, although mitochondrial and chloroplast DNA have features of prokaryotic DNA. The genome of mitochondria and chloroplasts is much smaller than that of present-day prokaryotes. During evolution of the eukaryote, many early mitochondrial and chloroplast genes apparently migrated to the eukaryotic nucleus. Many proteins, synthesized in the cytoplasm of eukaryotic cells, transfer to mitochondria or chloroplasts, where they play essential roles in energy production. Today, mitochondria and chloroplasts cannot live freely outside the eukaryotic cell and the eukaryotic cell cannot survive without its mitochondrial or chloroplast organelles.