Understanding Cells: Structure, Function, and MRS GREN

• Cells are the fundamental units constituting all living organisms.

• All living organisms consist of one or more cells.

• Cells are the basic structural and organizational units in organisms.

• Cells originate from pre-existing cells.

• Essential characteristics of living organisms can be remembered using the acronym MRS GREN:

• Movement

• Respiration

• Sensitivity

• Growth

• Reproduction

• Excretion

• Nutrition

• Cells contain organelles, which are small structures that perform specific functions.

• A micrometre is the unit used to measure cells due to their extremely small size.

Organelle Functions

• Cell membrane:
• Encloses and protects the cell.
• Regulates the entry and exit of substances (nicknamed "Gate").
• Mitochondria:
• Produces and supplies energy for the cell (nicknamed "Solar panels").
• Nucleus:
• The control center of the cell.
• Contains DNA and controls cell activities (nicknamed "Brain").
• Cytoplasm:
• A jelly-like substance inside cells where organelles move (nicknamed "Jelly").
• Chloroplasts:
• Contain chlorophyll and facilitate photosynthesis, converting sunlight into sugars and releasing oxygen (nicknamed "Food producers").
• Vacuole:
• Stores water and dissolved substances and is used when the cell needs water (nicknamed "Cactus").
• Cell wall:
• Protects and supports the cell, providing stiffness and shape (nicknamed "Protector").
• Ribosome:
• Produces proteins in the cell (nicknamed "Protein factory").

Unicellular vs Multicellular Organisms

• Organisms can be unicellular (single-celled) or multicellular.
• Unicellular organisms:
• Single-celled organisms perform all necessary functions (e.g., bacteria, protozoa, ciliate).
• Multicellular organisms:
• Consist of many cells with different cells performing varied functions (e.g., humans, dogs, animals).

Cell Structures Comparison

• Animal Cells Only:
• Centrosomes
• Lysosomes
• Animal and Plant Cells:
• Ribosome
• Nucleus
• Mitochondrion
• Cytoplasm
• Cell membrane
• Vacuole
• Plant Cells Only:
• Chloroplast
• Cell wall

Cellular Respiration

• Cellular respiration:
• Cells convert glucose and oxygen into energy (ATP), carbon dioxide, and water.
• To "respire" means to breathe or release energy from food.
• Cells need to grow, reproduce, produce energy, and remove waste.
• Cells require oxygen, water, nutrients (like glucose), and energy (ATP) to function.
• Cellular respiration occurs in the mitochondria.
• Respiration's purpose is to produce energy (ATP) for the cell.

Photosynthesis

• Photosynthesis:
• Plants use sunlight, carbon dioxide, and water to produce glucose and oxygen.
• Cellular respiration occurs in both plant and animal cells, while photosynthesis occurs only in plant cells.
• Cellular respiration makes energy (ATP) for cells, and photosynthesis makes food (glucose) for plants.
• Glucose and oxygen are needed for cellular respiration, while carbon dioxide, water, and sunlight are needed for photosynthesis.
• If mitochondria stop functioning, the cell will not produce enough energy (ATP) and may die.

Acquiring Oxygen

• Animals get oxygen from the air.
• Fish get oxygen from water through gills.
• Humans get oxygen from the air.
• Plants get oxygen from the air through stomata.

Cell Specialization

• Complex organisms have specialized cells with specific functions.
• Cells do not work independently; they are organized into tissues, organs, and organ systems for efficient collaboration.
• Cell specialization:
• Development of specific structures and functions for a particular role.
• Cells become specific types based on gene activation controlled by chemical signals.
• Cells specialize through differentiation, where genes turn on or off to shape their function.
• Cell organization:
• Cells → tissues → organs → organ systems → organisms

Tissue and Organ Organization

• Groups of similar cells form tissues.
• Groups of different tissues make up organs.
• Groups of organs form organ systems.
• Groups of organ systems form organisms.

Organ Systems

• Nervous System:
• Receives, processes, and responds to stimuli; includes the brain, spinal cord, and nerves.
• Cardiovascular System:
• Transports blood, oxygen, and nutrients throughout the body; includes the heart, blood vessels, and blood.
• Respiratory System:
• Facilitates gas exchange, taking in oxygen and releasing carbon dioxide; includes the lungs, airways, and diaphragm.
• Digestive System:
• Breaks down food into smaller molecules for energy; includes the mouth, esophagus, stomach, intestines, and liver.

Additional Notes

• Every plant cell has a vacuole.
• ATP is an energy carrier.
• CO2 is carbon dioxide.
• O2 is oxygen.
• H2O is water.
• Glucose is C6H12O6.