AP Biology 2.1 Cell Structure and Function Study Notes - New Syllabus Effective 2025
AP Biology 2.1 Cell Structure and Function Study Notes- New syllabus
AP Biology 2.1 Cell Structure and Function Study Notes – AP Biology – per latest AP Biology Syllabus.
LEARNING OBJECTIVE
Explain how the structure and function of subcellular components and organelles contribute to the function of cells.
Key Concepts:
- Subcellular Components
- Cell Structure & Function
- Cells & Surface Area
- Specialized Exchange Strategies
2.1.A.1 : Ribosome
Ribosome subunits are manufactured in the nucleus and consist of RNA molecules and proteins. The two subunits, labeled 60S and 40S, move across the nuclear envelope and into the cytoplasm where they are assembled into a sin gle 80S ribosome. (An S value, or Svedberg unit, expresses how readily a product forms a sediment in a centrifuge, with larger values representing larger and heavier products.) In the cytoplasm, ribosomes assist in the assembly of amino acids into proteins.
Some points regarding ribosomes are following: –
- Sites of protein synthesis
- Manufacture all proteins required/secreted by the cell
- Consists of RNA and other proteins
- Bind messenger RNA and transfer RNA to synthesize proteins
- Round structures consisting of 2 subunits:te large subunit and the small subunit
- Composed of RNA and proteins
- Can either be free floating or attached to the endoplasmic reticulum (ER)
2.1.A.3 : Endoplasmic Reticulum
The endoplasmic reticulum, or ER, consists of stacks of flattened sacs involved in the production of various materials. In cross section, they appear as a series of maze-like channels, often closely associated with the nucleus. When ribosomes are present, the ER (called rough ER) creates glycoproteins by attaching polysaccharide groups to polypeptides as they are assembled by the ribosomes. Smooth ER, without ribosomes, is responsible for vari ous activities, including the synthesis of lipids and hormones, especially in cells that produce these substances for export from the cell. In liver cells, smooth ER is involved in the breakdown of toxins, drugs, and toxic by-products from cellular reactions.
2.1.A.4 : Golgi complex
A Golgi apparatus (Golgi complex or Golgi body) is a group of flattened sacs arranged like a stack of bowls. They modify and package proteins and lipids into vesicles, small, spherically shaped sacs that bud from the out side surface of the Golgi apparatus. Vesicles often migrate to and merge with the plasma membrane, releasing their contents to the outside of the cell.
Some important points regarding golgi complex are following: –
- Process proteins
- Once the ribosomes on the rough ER have completed synthesizing proteins, the Golgi
bodies modify, process, and sort the products - packaging/distribution centers for materials destined to be sent out of cell
- Package final products into vesicles
■ Carry products to plasma membrane - Involved in production of lysosomes
2.1.A.5 : Mitochondria
Mitochondria carry out aerobic respiration, a process in which energy (in the form of ATP) is obtained from carbohydrates.
Some important points regarding mitochondria are following: –
- “Powerhouse of the ceil”
- Responsible for converting the energy from organic molecules into useful energy for the cell
- Energy molecule in the cell is adenosine triphosphate (ATP)
- Unique oblong shape and characteristic double membrane consisting of an inner portion and an outer portion
- Inner membrane forms folds called cristae
■ Separates innermost area (called the matrix) from the intermembrane space
■ Outer membrane separates the intermembrane space from the cytoplasm
■ Production of ATP done on the cristae
2.1.A.6 : Lysosome
Lysosomes are vesicles from a Golgi apparatus that contain digestive enzymes. They break down food, cellular debris, and foreign invaders such as bacteria. A low pH (acidic), favorable to the activity of the enzymes, is main tained inside the lysosome. As a result, any enzyme that might escape from the lysosome remains inactive in the neutral pH of the cytosol. Lysosomes do not occur in plant cells.
Some important points: –
- Tiny sacs that carry digestive enzymes
- Break down old/worn out organelles/debris/large ingested particles
- Cells clean-up crew
- Keep cytoplasm clear of unnecessary flotsam
- Sometimes contain hydrolytic enzymes that function only at an acidic pH, which is enclosed inside the lumen of the lysosome
2.1.A.7 : Vacuoles
Vacuoles and vesicles are fluid-filled, membrane-bound bodies.
- Transport vesicles move materials between organelles or between organelles and the plasma membrane.
- Food vacuoles are temporary receptacles of nutrients. Food vacuoles often merge with lysosomes, whose digestive enzymes break down the food.
- Storage vacuoles in plants store starch, pigments, and toxic substances (nicotine, for example).
- Central vacuoles are large bodies occupying most of the interior of certain plant cells. When fully filled, they exert turgor, or pressure, on the cell walls, thus maintaining rigidity in the cell. They also store nutrients and carry out functions otherwise assumed by lysosomes in animal cells.
- Contractile vacuoles are specialized organelles in single-celled organisms that collect and pump excess water out of the cell.
2.1.A.8 : Chloroplasts
“Chloroplast is an organelle that contains the photosynthetic pigment chlorophyll that captures sunlight and converts it into useful energy, thereby, releasing oxygen from water. “
Plants form the basis of all life on earth and are known as producers. Plant cells contain structures known as plastids which are absent in animal cells. These plastids are double-membraned cell organelles which play a primary role in the manufacturing and storing of food. There are three types of plastids –
- Chromoplasts- They are the colour plastids, found in all flowers, fruits and are mainly responsible for their distinctive colours.
- Chloroplasts- They are green coloured plastids, which comprise green-coloured pigments within the plant cell and are called chlorophyll.
- Leucoplasts- They are colourless plastids and are mainly used for the storage of starch, lipids and proteins within the plant cell.
Structure
The chloroplast diagram below represents the chloroplast structure mentioning the different parts of the chloroplast. The parts of a chloroplast such as the inner membrane, outer membrane, intermembrane space, thylakoid membrane, stroma and lamella can be clearly marked out.
Functions of Chloroplast
Following are the important chloroplast functions:
- The most important function of the chloroplast is to synthesise food by the process of photosynthesis.
- Absorbs light energy and converts it into chemical energy.
- Chloroplast has a structure called chlorophyll which functions by trapping the solar energy and is used for the synthesis of food in all green plants.
- Produces NADPH and molecular oxygen (O2) by photolysis of water.
- Produces ATP – Adenosine triphosphate by the process of photosynthesis.
- The carbon dioxide (CO2) obtained from the air is used to generate carbon and sugar during the Calvin Cycle or dark reaction of photosynthesis.