Bio Test Revision

Cell Structure

Prokaryotes:

• Single-celled organisms

• Lack organelles

• No nucleus (nucleoid), 

• Genetic material in a nucleoid region

• Smaller in size (0.1 to 5 micrometres)kin

• Simple organization with cell membrane, cytoplasm, and cell wall

• Reproduce through binary fission

• Found in bacteria and archaea

• Circular chromosomes

Eukaryotes:

• Complex organisms

• Have a true nucleus and membrane-bound organelles

• Larger in size (10 to 100 micrometres)

• More structured organization with internal structures like mitochondria, endoplasmic reticulum, etc.

• Reproduce through both asexual and sexual reproduction

• Include plants, animals, fungi, and protists

• Linear chromosomes

Here are the major organelles and their functions in a cell:

1. Nucleus:

   - Function: Controls cell activities and stores genetic material (DNA).

   - Contains: DNA, nucleolus.

2. Mitochondria:

   - Function: Powerhouse of the cell, produces energy through cellular respiration.

   - Contains: Inner membrane, outer membrane, matrix.

3. Chloroplasts (Found in plant cells):

   - Function: Site of photosynthesis, converts sunlight into chemical energy.

   - Contains: Chlorophyll, thylakoid membranes, and stroma.

4. Rough and Smooth Endoplasmic Reticulum (ER):

   - Function (Rough ER): Involved in protein synthesis, has ribosomes attached to its surface.

   - Function (Smooth ER): Involved in lipid metabolism, detoxification, and calcium storage.

   - Contains: Membrane network.

5. Golgi Body (Golgi Apparatus):

   - Function: Modifies, sorts, and packages proteins and lipids for transport within or outside the cell.

   - Contains: Stacked membrane sacs (cisternae).

6. Ribosomes:

   - Function: Site of protein synthesis, where amino acids are assembled into protein chains.

   - Found: Floating freely in the cytoplasm or attached to the rough ER.

7. Vacuoles:

   - Function: Store water, ions, nutrients, and waste materials; can also provide structural support.

   - Found: Central vacuole in plant cells, smaller vacuoles in animal cells.

8. Cell Wall (Found in plant cells):

   - Function: Provides structural support and protection to the cell.

   - Contains: Cellulose fibres.

9. Cytoplasm:

• Function: Provide a medium for biochemical regions to take place, and maintain the shape of a cell (animals especially

• Contains: Fluid (water and salt) fills the cell and encases all other organelles

10. Cell membrane:

• Function: 

• Contains: 

Cellular respiration

Cellular Respiration:

• Glucose + Oxygen →  carbon dioxide + water + energy

Cellular respiration occurs in the mitochondria of the cell. It is a process where glucose and oxygen are broken down to produce carbon dioxide, water, and ATP (adenosine triphosphate), which is the energy currency of the cell.

The energy that is released during cellular respiration is used to produce ATP. ATP is a molecule that stores and transports energy within the cell. It is used to power various cellular processes and reactions.

ATP is produced from ADP (adenosine diphosphate) and P (inorganic phosphate) through a process called phosphorylation. In this process, a phosphate group is added to ADP to form ATP. This conversion of ADP to ATP occurs in the mitochondria through a series of chemical reactions known as the electron transport chain and oxidative phosphorylation.

The breakdown of one glucose molecule in cellular respiration can produce up to 36-38 molecules of ATP, depending on the efficiency of the process.

Anaerobic Respiration:

In humans, the word equation for anaerobic respiration is:

• Glucose → Lactic Acid + ATP

During anaerobic respiration in humans, glucose is converted into lactic acid, and a small amount of ATP is produced.

In yeast and bacteria, the word equation for anaerobic respiration is:

• Glucose → Ethanol + Carbon Dioxide + ATP

In yeast and bacteria, anaerobic respiration, also known as fermentation, involves the conversion of glucose into ethanol, carbon dioxide, and a small amount of ATP.

Main Differences between Aerobic and Anaerobic Respiration:

Aerobic Respiration:

1. Requires oxygen.

2. Occurs in the mitochondria.

3. Produces a large amount of ATP (36-38 molecules of ATP per glucose molecule).

4. Produces carbon dioxide and water as byproducts.

Anaerobic Respiration:

1. Does not require oxygen.

2. Occurs in the cytoplasm (in humans) or specialized organelles (in yeast and bacteria).

3. Produces a smaller amount of ATP (2 molecules of ATP per glucose molecule in humans, and a small amount in yeast and bacteria).

4. Produces lactic acid (in humans) or ethanol and carbon dioxide (in yeast and bacteria) as byproducts.

Structure of the Cell Membrane

The cell membrane, also known as the plasma membrane, is a selectively permeable barrier that surrounds the cell. It consists of a phospholipid bilayer with embedded proteins and carbohydrates.

Phospholipid Bilayer:

   - The phospholipid bilayer forms the basic framework of the cell membrane.

   - It is composed of two layers of phospholipids, with their hydrophilic (water-loving)     phosphate heads facing outward and their hydrophobic (water-repelling) fatty acid tails facing inward, creating a stable barrier.

Proteins:

   - Integral Proteins: These proteins are embedded within the phospholipid bilayer and span across the entire membrane. They play various roles, such as transporters, channels, receptors, and enzymes.

   - Peripheral Proteins: These proteins are loosely attached to the surface of the cell membrane and do not extend into the hydrophobic core of the lipid bilayer. They provide support, signalling, and other functions.

Carbohydrates:

   - Carbohydrates are attached to the outer surface of the cell membrane, forming glycoproteins and glycolipids.

   - They serve as recognition sites for cell-cell interactions, immune responses, and cell signalling.

Movement of Substances across the Cell Membrane:

Diffusion:

   - Definition: The passive movement of molecules from an area of high concentration to an area of low concentration, down their concentration gradient.

   - Does not require energy.

   - Small, non-polar molecules, such as oxygen and carbon dioxide, can diffuse directly through the cell membrane.

Facilitated Diffusion:

   - Definition: The passive movement of molecules across the cell membrane with the help of transport proteins.

   - Does not require energy.

   - Large or charged molecules, such as glucose and ions, rely on integral membrane proteins called transporters or channels to facilitate their diffusion.

Osmosis:

   - Definition: The diffusion of water molecules across a selectively permeable membrane, from an area of lower solute concentration (more water) to an area of higher solute concentration (less water).

   - Does not require energy.

   - Water moves through specialized water channels called aquaporins.

Active Transport:

   - Definition: The movement of molecules against their concentration gradient, from an area of low concentration to an area of high concentration.

   - Requires energy (in the form of ATP).

   - Involves integral membrane proteins called pumps or transporters.

   - Examples include the sodium-potassium pump and proton pump.

• Endocytosis:

   - Definition: The process by which cells engulf substances from the external environment into the cell by forming vesicles.

   - Requires energy (ATP).

   - Types of endocytosis include pinocytosis (cell drinking) and phagocytosis (cell eating).

• Exocytosis:

   - Definition: The process by which cells release substances from the cell by fusing vesicles with the cell membrane.

   - Requires energy (ATP).

   - Examples include the secretion of hormones or neurotransmitters.

Microorganisms

Types of Microorganisms

• Bacteria, fungi, and protists are the three main types of microorganisms.

Importance of Gut Health

• Gut health refers to the balance and function of microorganisms in the digestive system.

• Imbalanced gut microbiota can contribute to gastrointestinal disorders like IBS and IBD.

• Maintaining a healthy gut can be achieved through a balanced diet rich in fiber, probiotics, and prebiotics.

Microorganisms and Their Uses for Humans

• Microorganisms are used in medicine (e.g., antibiotics, vaccines), food production (e.g., fermentation), environmental cleanup (bioremediation), and biotechnology (e.g., genetic engineering).

Bacterial Reproduction

• Bacteria reproduce through binary fission, where a single cell divides into two identical daughter cells.
  

Conditions Required for Bacterial Growth

• Bacteria require nutrients, moisture, proper temperature, specific pH levels, and oxygen (depending on the type) for growth.

Processes to Reduce Bacterial Contamination in Food Handling/Preparation

• Handwashing and proper cooking are two common methods to reduce bacterial contamination in food handling/preparation.
  

Processes to Stop Bacterial Growth in Food

• Refrigeration and freezing are processes used to slow down or stop bacterial growth in food.