Cells

Fluid mosaic model

Fluid mosaic model

• cell membrane is fluid in that the phospholipids and proteins are not stationary and but can move rapidly across the surface of the membrane

• cell membrane is a mosaic in that many different protein molecules are randomly scattered and embedded throughout the phospholipid bilayer

Cell membrane

• partially permeable

• controls how substances move in and out of the cell

Nucleus

• contains nuclear envelope: separates nucleus from cytoplasm

• Contains nucleolus: synthesises ribosomes

• Contains DNA

• Controls the activities of the cell

Rough endoplasmic reticulum

protein synthesis

Smooth endoplasmic reticulum

lipid synthesis

Golgi apparatus

chemically modifies products received from the ER and packages them before sending them to destinations in and out of the cell using vesicles

Lysosomes

• contains hydrolytic enzymes

• to digest materials made in the cell or taken in from outside by phagocytosis

• to digest worn-out organelles in the cell by autophagy

Animal vacuole

• formed either by pinching off part of the cell membrane or by enlargement of a vesicle from the Golgi apparatus

• Usually relatively smaller and exist temporarily

  • Food vacuoles: formed by phagocytosis

Plant vacuole

• large central vacuole is permanent and occupies over 80% of the cell volume

• Enclosed by a single partially permeable membrane called the tonoplast

• Filled with cell sap

• storage of nutrients and inorganic ions

• disposal sites for metabolic by-product that would endanger the cell if they accumulated in the cytosol

Mitochondria

• involved in aerobic respiration

• abundant in metabolically active cells (muscle, liver cells)

Chloroplasts

• contains chlorophyll

• contains thylakoids and stroma

Ribosome

• may occur as free ribosomes suspended in the cytosol or bound to the RER

• Site of polypeptide synthesis

• Free ribosomes generally make proteins that will function within the cytosol

• Bound ribosomes generally make proteins that are destined for insertion into membranes, for packaging within certain organelles, or for export from the cell

Centrioles

plays a role in cell division in animal cells

Describe the process of protein synthesis and secretion

• polypeptide chains are synthesised at the ribosomes and folded at the RER

• transport vesicles containing substances made by the ER pinch off from the ER

• These transport vesicles then fuse and then release their substances into the Golgi apparatus

• These substances are chemically modified and packaged inside the Golgi apparatus

• Secretory vesicles containing these modified substances are pinched off from the Golgi apparatus

• The secretory vesicles move towards and fuse with the cell membrane, releasing the substances outside the cell by exocytosis

Describe the formation of lysosomes

• enzyme contents are synthesised on the RER and transported via transport vesicles to the Golgi apparatus for further processing

• a vesicle containing the processed enzymes buds off from the Golgi apparatus, forming a lysosome

Similarities and differences between plant and animal cell

Similarities: both cells contain cell membrane, mitochondria, nucleus and cytoplasm

Differences:

Features	Plant	Animal
Cell wall	Surrounded by cell wall in addition to cell membrane	Cell wall is absent, only surrounded by the cell membrane
Chloroplasts	Present in large numbers in photosynthetic cells	Absent
Centrioles	Absent	Present
Vacuole	Present as a single, large and central vacuole	small and numerous

Root hair cell

Presence of long narrow extension

• For the absorption of water and mineral salts

  • Increase SA:V ratio which increases the rate of diffusion of mineral salts and osmosis

Red blood cell

Transport oxygen to other body cells

• Presence of haemoglobin

  • haemoglobin combines with oxygen

• Absence of nucleus

  • allows more haemoglobin to be packed into the cell

• Biconcave shape

  • Increase SA:V ratio to increase rate of diffusion of oxygen and carbon dioxide

Muscle cell

Contains many nuclei and mitochondria

• Has mitochondria to provide energy for the contraction of muscle cell

Level of complexity

Macromolecule → Organelle → Cell → Tissue → Organ → Organ System