2.1 Cell structure

Describe and compare the structure of a plant cell with an animal cell, limited to: cell wall, cell membrane, nucleus, cytoplasm, chloroplasts, ribosomes, mitochondria, vacuoles. #

Plant Cell:

1. Cell Wall:

   – Plant cells have a rigid cell wall composed primarily of cellulose.

   – The cell wall provides structural support and protection to the plant cell.

2. Cell Membrane:

   – Plant cells, like animal cells, have a cell membrane.

   – The cell membrane regulates the movement of substances in and out of the cell and helps maintain cell shape and integrity.

3. Nucleus:

   – Plant cells have a nucleus, which is the control center of the cell.

   – The nucleus contains the genetic material (DNA) and is responsible for regulating cell activities and cell division.

4. Cytoplasm:

   – Plant cells, similar to animal cells, have a cytoplasm.

   – The cytoplasm is a gel-like substance that fills the cell and houses various organelles.

5. Chloroplasts:

   – Plant cells have chloroplasts, which are specialized organelles responsible for photosynthesis.

   – Chloroplasts contain chlorophyll, a pigment that captures light energy used to convert carbon dioxide and water into glucose and oxygen.

6. Ribosomes:

   – Plant cells, like animal cells, contain ribosomes.

   – Ribosomes are responsible for protein synthesis within the cell.

7. Mitochondria:

   – Plant cells have mitochondria, which are organelles involved in cellular respiration.

   – Mitochondria generate energy (ATP) through the breakdown of glucose and other nutrients.

8. Vacuoles:

   – Plant cells typically have a large central vacuole.

   – The central vacuole stores water, nutrients, and waste materials, and helps maintain turgor pressure, providing structural support to the plant cell.

Animal Cell:

1. Cell Membrane:

   – Animal cells have a cell membrane that controls the movement of substances in and out of the cell.

2. Nucleus:

   – Animal cells also have a nucleus, which contains the genetic material (DNA) and regulates cell activities.

3. Cytoplasm:

   – Animal cells contain cytoplasm, a gel-like substance that fills the cell and houses various organelles.

4. Ribosomes:

   – Animal cells contain ribosomes responsible for protein synthesis.

5. Mitochondria:

   – Animal cells have mitochondria, which generate energy (ATP) through cellular respiration.

6. Vacuoles:

   – Animal cells may have smaller vacuoles, but they are not as prominent as in plant cells.

The main structural differences between plant and animal cells are the presence of a cell wall, chloroplasts, and a large central vacuole in plant cells, which are absent in animal cells. Plant cells also have chloroplasts for photosynthesis, while animal cells do not. Both plant and animal cells share common organelles such as the cell membrane, nucleus, cytoplasm, ribosomes, and mitochondria, which are involved in fundamental cellular processes.

Describe the structure of a bacterial cell, limited to: cell wall, cell membrane, cytoplasm, ribosomes, circular DNA, plasmids. #

The structure of a bacterial cell is relatively simple compared to eukaryotic cells. Here is a description of the main components of a bacterial cell:

1. Cell Wall:

   – Bacterial cells have a cell wall surrounding the cell membrane.

   – The cell wall provides structural support and protection to the bacterial cell.

   – The composition of the cell wall varies among different types of bacteria. Some bacteria have a thick cell wall made of peptidoglycan, while others have a thinner cell wall or lack a cell wall entirely.

2. Cell Membrane:

   – Bacterial cells have a cell membrane, also known as the plasma membrane.

   – The cell membrane is a semi-permeable barrier that regulates the movement of substances in and out of the cell.

   – It plays a crucial role in nutrient uptake, waste elimination, and energy production.

3. Cytoplasm:

   – The cytoplasm is a gel-like substance that fills the bacterial cell.

   – It contains various components such as enzymes, nutrients, ions, and water.

   – Metabolic reactions, protein synthesis, and DNA replication occur within the cytoplasm.

4. Ribosomes:

   – Bacterial cells contain ribosomes, which are responsible for protein synthesis.

   – Ribosomes in bacterial cells are smaller than those in eukaryotic cells, typically measuring 70S (svedberg units).

5. Circular DNA:

   – Bacterial cells have a single, circular DNA molecule located in the cytoplasm.

   – This circular DNA contains the genetic information necessary for bacterial cell functioning and replication.

   – The DNA molecule carries the bacterial genes and is not housed within a nucleus as seen in eukaryotic cells.

6. Plasmids:

   – Plasmids are small, circular DNA molecules separate from the main bacterial chromosome.

   – Bacterial cells can contain one or multiple plasmids.

   – Plasmids often carry additional genes that provide advantages to bacteria, such as antibiotic resistance or the ability to produce certain proteins.

These components collectively contribute to the structure and function of a bacterial cell. Bacteria, as prokaryotic organisms, have a simpler cellular organization compared to eukaryotic cells, lacking membrane-bound organelles and having a smaller genome. However, they are highly adaptable and possess unique features that enable them to thrive in diverse environments.

Identify the cell structures listed in 2.1.1 and 2.1.2 in diagrams and images of plant, animal and bacterial cells. #

Describe the functions of the structures listed in 2.1.1 and 2.1.2 in plant, animal and bacterial cells. #

1. Cell Wall:

   – Plant Cell: The cell wall provides structural support and rigidity to plant cells, protecting them from mechanical stress.

   – Animal Cell: Animal cells lack a cell wall, relying on the cell membrane for shape and structure.

   – Bacterial Cell: The cell wall in bacteria provides shape, protection, and structural support to the cell. It helps maintain cell integrity and prevents the cell from bursting or collapsing due to osmotic pressure.

2. Cell Membrane (Plasma Membrane):

   – Plant Cell: The cell membrane regulates the movement of substances in and out of plant cells, maintaining cellular homeostasis.

   – Animal Cell: The cell membrane in animal cells controls the exchange of materials and helps maintain cell integrity.

   – Bacterial Cell: The cell membrane in bacterial cells acts as a selectively permeable barrier, controlling the transport of nutrients, waste products, and other molecules in and out of the cell.

3. Nucleus:

   – Plant Cell: The nucleus houses the genetic material (DNA) in plant cells, controlling cellular activities.

   – Animal Cell: The nucleus serves as the control center of animal cells, containing the genetic material and regulating cellular processes.

   – Bacterial Cell: Bacterial cells lack a distinct nucleus. Instead, their DNA is present as a single, circular chromosome in the cytoplasm. The DNA controls cellular activities and carries the genetic information for bacterial replication and functions.

4. Cytoplasm:

   – Plant Cell: The cytoplasm in plant cells provides a medium for cellular reactions, transport of substances, and supports cell structure.

   – Animal Cell: Animal cell cytoplasm performs similar functions to plant cells, providing a medium for cellular processes and supporting cell structure.

   – Bacterial Cell: The cytoplasm in bacterial cells houses various components, including enzymes, ribosomes, and the bacterial chromosome. It is involved in cellular metabolism, protein synthesis, and other biochemical reactions.

5. Chloroplasts:

   – Plant Cell: Chloroplasts are present in plant cells and are the sites of photosynthesis. They convert light energy into chemical energy (glucose) using chlorophyll and other pigments.

   – Animal Cell: Animal cells do not contain chloroplasts since they cannot perform photosynthesis.

   – Bacterial Cell: Bacterial cells lack chloroplasts and are incapable of photosynthesis.

6. Ribosomes:

   – Plant Cell: Ribosomes in plant cells are responsible for protein synthesis, reading the genetic code and translating it into proteins.

   – Animal Cell: Animal cells have ribosomes that perform the same function as in plant cells, synthesizing proteins based on genetic instructions.

   – Bacterial Cell: Bacterial cells also have ribosomes involved in protein synthesis. However, bacterial ribosomes are smaller and differ slightly in structure from eukaryotic ribosomes.

7. Mitochondria:

   – Plant Cell: Mitochondria in plant cells are the sites of cellular respiration, generating ATP through the breakdown of organic molecules.

   – Animal Cell: Animal cells have mitochondria that perform the same function as in plant cells, producing ATP through cellular respiration.

   – Bacterial Cell: Bacterial cells may have small infoldings in the cell membrane that function similarly to mitochondria, carrying out cellular respiration and generating ATP.

8. Vacuoles:

   – Plant Cell: Plant cells often have a large central vacuole that stores water, nutrients, pigments, and waste products. It helps maintain cell turgidity and acts as a storage compartment.

   – Animal Cell: Animal cells may have smaller vacuoles, but they

 are not as prominent as in plant cells.

   – Bacterial Cell: Bacterial cells can have small vacuoles or vesicles that store various substances such as ions, nutrients, and toxins. These vacuoles play a role in osmoregulation and storage.

It’s important to note that bacterial cells differ significantly from plant and animal cells in terms of their structure, lack of membrane-bound organelles, and smaller genome size.

State that new cells are produced by division of existing cells. #

New cells are indeed produced by the division of existing cells. This process, known as cell division or cell reproduction, is a fundamental mechanism by which organisms grow, develop, and replace damaged or old cells. Cell division ensures the continuity of life and allows for the maintenance and repair of tissues and organs.

There are two main types of cell division: mitosis and meiosis. Mitosis is a process of cell division that occurs in somatic cells, resulting in the formation of two genetically identical daughter cells. This type of cell division is involved in growth, tissue repair, and asexual reproduction in organisms.

Meiosis, on the other hand, is a specialized form of cell division that occurs in reproductive cells (gametes). It involves two rounds of division, resulting in the production of four haploid cells (gametes) with half the number of chromosomes compared to the parent cell. Meiosis is crucial for sexual reproduction and the generation of genetic diversity.

Regardless of the type of cell division, the process involves the replication and segregation of genetic material (DNA) and the subsequent division of the cytoplasm, leading to the formation of two daughter cells. This ensures that each new cell receives a complete set of genetic information and the necessary cellular components to carry out its functions.

Overall, the division of existing cells is a fundamental process in biology, playing a vital role in growth, development, tissue maintenance, and reproduction.

State that specialised cells have specific functions, limited to: #

(a) ciliated cells – movement of mucus in the trachea and bronchi

(b) root hair cells – absorption

(c) palisade mesophyll cells – photosynthesis

(d) neurones – conduction of electrical impulses

(e) red blood cells – transport of oxygen

(f) sperm and egg cells (gametes) – reproduction

Specialized cells in organisms have specific functions that contribute to the overall functioning and survival of the organism. 

(a) Ciliated cells: Ciliated cells are found in the trachea and bronchi of the respiratory system. Their function is to move mucus and trapped particles out of the airways through coordinated beating of cilia. This mechanism helps to protect the lungs by preventing the buildup of mucus and facilitating the removal of foreign particles.

(b) Root hair cells: Root hair cells are found in the roots of plants. Their specialized structure includes long, thin extensions called root hairs that increase the surface area for absorption. Their main function is to absorb water and nutrients from the soil, facilitating the uptake of essential substances for plant growth and metabolism.

(c) Palisade mesophyll cells: Palisade mesophyll cells are present in the leaves of plants, particularly in the upper layer of the leaf called the mesophyll. These cells are responsible for photosynthesis, the process by which plants convert light energy into chemical energy (glucose). Palisade mesophyll cells contain numerous chloroplasts, which contain chlorophyll and other pigments necessary for capturing light energy.

(d) Neurons: Neurons, also known as nerve cells, are specialized cells of the nervous system. Their primary function is to transmit and conduct electrical impulses or signals throughout the body. Neurons are responsible for coordinating and controlling various bodily functions, including sensory perception, motor control, and information processing.

(e) Red blood cells: Red blood cells, or erythrocytes, are specialized cells found in the blood. Their main function is to transport oxygen from the lungs to the body’s tissues and remove carbon dioxide, a waste product of cellular respiration. Red blood cells contain a protein called hemoglobin, which binds and carries oxygen throughout the body.

(f) Sperm and egg cells (gametes): Sperm cells (spermatozoa) and egg cells (ova) are specialized sex cells or gametes involved in sexual reproduction. Their primary function is to fuse during fertilization, resulting in the formation of a new organism with a unique combination of genetic material from both parents. Sperm cells are specialized for mobility and delivering genetic material to the egg cell, while egg cells provide a nutrient-rich environment for fertilization and subsequent development.

These examples highlight how specialized cells have specific functions that contribute to the overall functioning, growth, and reproduction of organisms. Each specialized cell type is adapted to carry out its specific role, allowing for the efficient performance of complex biological processes.

Describe the meaning of the terms: cell, tissue, organ, organ system and organism as illustrated by examples given in the syllabus. #

1. Cell: A cell is the basic structural and functional unit of life. It is the smallest unit of an organism that can carry out all the necessary processes for life, including metabolism, reproduction, and response to stimuli. Cells can vary in size, shape, and specialized functions, but they all have a cell membrane, cytoplasm, and genetic material (DNA).

2. Tissue: Tissue refers to a group or collection of similar cells that work together to perform a specific function. Cells within a tissue share a common structure and function. There are four main types of tissues in complex organisms: epithelial tissue (covers and protects body surfaces), connective tissue (supports and connects various body parts), muscle tissue (enables movement), and nervous tissue (transmits and processes information).

3. Organ: An organ is a structure made up of different types of tissues that work together to perform a specific function or functions. Organs have a distinct shape and organization and carry out specialized tasks necessary for the proper functioning of the organism. Examples of organs include the heart, lungs, liver, brain, and kidneys.

4. Organ System: An organ system refers to a group of organs that work together to perform a common set of functions, contributing to the overall well-being and survival of an organism. Each organ within a system has a specific role, and their coordinated efforts are essential for maintaining homeostasis and ensuring the proper functioning of the organism. Examples of organ systems include the circulatory system, respiratory system, digestive system, nervous system, and skeletal system.

5. Organism: An organism is a complete living individual, whether it is a single-celled organism or a complex multicellular organism. It is a biological entity capable of carrying out all the essential life processes, such as growth, reproduction, metabolism, and response to stimuli. Organisms can be unicellular (composed of a single cell) or multicellular (composed of multiple cells organized into tissues, organs, and systems). Examples of organisms include bacteria, plants, animals, and humans.

In summary, cells are the building blocks of life, tissues are groups of cells working together, organs are composed of different tissues and have specific functions, organ systems are groups of organs working together, and organisms are complete living individuals capable of carrying out essential life processes. These hierarchical levels of organization contribute to the complexity and functionality of living organisms.