Major cellular organelles

How many cells make up the human body

• 50–100 trillion cells

• High diversity in structure and function

What is the smallest structural and functional unit of life

• The cell

How many cell types exist in the human body

• 250+ types

What are examples of different cell types and their features

• Fibroblasts

• Erythrocytes — some of the smallest in the body

• Epithelial cells — tightly joined; form a barrier; protect underlying tissue

• Skeletal muscle cells

• Smooth muscle cells

• Fat cells

• Macrophages

• Nerve cells — some of the largest; up to 1 m long from spine to big toe

What functions are cells able to perform

• Take in oxygen

• Take in nutrients

• Remove waste

• Respond to the environment

• Reproduce

• Perform specialised functions

• Keep the cell and organism alive

What does the activity of the organism depend on

• Individual activities of cells

• Combined activities of cells

What is homeostasis

• Maintenance of a stable internal environment

What happens if homeostasis is not achieved

• Underlies disease processes

• Cell function becomes impaired

What features are common to all cells

• Plasma membrane

• Cytoplasm

• Nucleus

What are organelles

• “Little organs” found within a cell

• Each organelle has a specific function

How do cells become specialised for their unique roles

• They gain individual organelles

• These organelles enable their specific function

What is the cytoplasm

• Watery space between the plasma membrane and the nucleus

What is the cytoplasm composed of

• Cytosol (intracellular fluid, ICF)

What does the cytoplasm contain

• Cellular organelles

• Dissolved solutes

What is cytosol

• The intracellular fluid (ICF) within the cytoplas

What is the nucleus

• The largest organelle in the cell

What does the nucleus house

• DNA

What does DNA provide for the cell

• Instructions for cell function

• Instructions for protein synthesis

Why is the nucleus called the “control center”

• It stores DNA

• DNA directs cell activities, especially protein synthesis

What happens if a cell does not have a nucleus

• It cannot reproduce

Which mature cell type lacks a nucleus

• Red blood cells (RBCs)

Why must the body continually make new RBCs

• Mature RBCs have no nucleus and cannot reproduce

What are ribosomes composed of

• Protein

What is the function of ribosomes

• Site of protein synthesis

What are free ribosomes

• Ribosomes floating in the cytoso

What do free ribosomes produce

• Proteins for use inside the cell

What are membrane‑bound ribosomes

• Ribosomes attached to the endoplasmic reticulum

What do membrane‑bound ribosomes produce

• Proteins for export out of the cell

What is the endoplasmic reticulum (ER)

• Interconnected tubes

• Continuous with the nucleus

What are the functions of the endoplasmic reticulum

• Synthesis

• Storage

• Transport

• Detoxification

What is the Rough Endoplasmic Reticulum (RER) studded with

• Ribosomes

What is the main function of ribosomes on the RER

• Produce proteins for export out of the cell

How does the RER modify proteins

• Folds long protein strands into their 3D functional shape

Where does the RER transport proteins

• To the end of the RER

• Into vesicles

• To the Golgi apparatus

What happens to proteins after the Golgi apparatus processes them

• Exported to the plasma membrane

• Released outside the cell via exocytosis

Which cells have extensive RER

• Secretory cells

• Example: liver cells producing many blood proteins

What distinguishes Smooth Endoplasmic Reticulum (SER) from RER

• No ribosomes attached

What does the SER synthesise

• Lipids

• Cholesterol

• Steroid‑based hormones

What other functions does the SER perform

• Detoxification

• Storage of calcium ions

What happens to substances made in the SER

• Packaged into vesicles

• Passed to the Golgi apparatus

Which cells contain large amounts of SER

• Cells that produce steroid‑based hormones

• Example: cells of the testes

What is the Golgi apparatus commonly called

• “The traffic director

What is the structure of the Golgi apparatus

• Stacks of flattened sacs

What are the main functions of the Golgi apparatus

• Modify proteins and lipids

• Concentrate proteins and lipids

• Package proteins and lipids

What does the Golgi apparatus form

• Vesicles

Where can vesicles from the Golgi be distributed

• Within the cell

• Inserted into the plasma membrane

• Moved to the plasma membrane for export by exocytosis

What is Pathway 1 of Golgi vesicle distribution

• Vesicle becomes a lysosome

What is Pathway 2 of Golgi vesicle distribution

• Vesicle membrane becomes part of the plasma membrane

What is Pathway 3 of Golgi vesicle distribution

• Vesicle contents are exported out of the cell by exocytosis

What process releases vesicle contents outside the cell

• Exocytosis

In which cells is the Golgi apparatus present in large numbers

• Cells that produce and secrete proteins

What are examples of cells with abundant Golgi apparatus

• Salivary gland cells

• Pancreatic cells

What is the nickname for mitochondria

• “The power house”

What is the shape of mitochondria

• Bean‑shaped organelle

Where are the mitochondria’s enzymes located

• On the surface of the inner membrane

What is the main function of mitochondria

• Cellular respiration

• Releases energy in the form of ATP (adenosine triphosphate)

Why is ATP important

• Without ATP, cells cannot supply energy to work

What determines the number of mitochondria in a cell

• The cell’s energy requirements

Which cells contain large numbers of mitochondria

• Highly active cells

• Example: skeletal muscle cells

Why do skeletal muscle cells have many mitochondria

• They have a large demand for energy

What are lysosomes commonly called

• “The demolition crew”

What is the structure of lysosomes

• Membrane‑enclosed spheres (sacs)

What do lysosomes contain

• Lysosomal enzymes

What is the main function of lysosomal enzymes

• Digest biological material

What types of material do lysosomes digest

• Proteins

• Cell debris

What recycling role do lysosomes perform

• Break down and recycle molecules

How do lysosomes contribute to cell defence

• Dispose of invading bacteria

• Dispose of viruses

• Dispose of toxins

What can lysosomes engulf inside the cell

• Damaged organelles

Which white blood cells contain many lysosomes

• Macrophages

Why do macrophages contain a large number of lysosomes

• They digest and destroy foreign material

• They break down bacteria, viruses, and debris

What are cilia

• Motile cellular extensions on the top of cells

How do cilia move

• Sweep in a wave‑like manner

What is the function of cilia

• Move materials across the cell surface

What are microvilli

• Minute finger‑like extensions of the plasma membrane

• Project from the cell surface

What is the main function of microvilli

• Increase the surface area of the cell

How do microvilli compare in size to cilia

• Smaller than cilia

What do microvilli look like

• Little shaggy hair

Where are microvilli especially important

• Intestines

• Kidneys

Why are microvilli important in these organs

• Increase the absorptive ability of the cell