Biology — Cell Structure & Organelles

What is a membrane-bound organelle?

a sub-compartment inside a cell wrapped in its own membrane

Which type of cell has membrane-bound organelles?

eukaryotic cells

What three parts work together to maintain a cell's shape?

the plasma membrane, the cytosol, and the cytoskeleton

What is the plasma membrane?

the outer boundary of the cell

What is the plasma membrane made of?

a bilayer of phospholipids and proteins

What does it mean that the plasma membrane is a selective barrier?

it lets only specific substances in or out

What is a phospholipid?

a lipid with a hydrophilic head and a hydrophobic tail

What does hydrophilic mean?

water-attracting

What does hydrophobic mean?

water-avoiding

How do phospholipids arrange in a membrane?

heads face the watery outside and inside, while the tails point inward away from water

What is the cytosol?

the gel-like, water-based fluid that fills the inside of the cell

What is the difference between cytosol and cytoplasm?

cytosol is the fluid alone, while cytoplasm is the cytosol plus everything in it

What is the cytoskeleton?

a network of protein fibres running through the cytoplasm

What does the cytoskeleton do?

it gives the cell shape, holds organelles in place, and enables movement and transport

Why can the cytoskeleton change shape?

it can be broken down and rebuilt, which helps with cell division and movement

How is a cell's shape linked to its function?

specialised shapes suit specialised jobs, like nerve cells branching to relay signals

What is the nucleus?

a membrane-bound organelle that holds the cell's DNA

What surrounds the nucleus?

the nuclear membrane, which has pores

How is DNA organised inside the nucleus?

into linear structures called chromosomes

What are ribosomes?

cell parts that build proteins

Where are ribosomes found?

free in the cytosol, or attached to the endoplasmic reticulum

Why are proteins important to a cell?

they are vital for nearly all cell functions

What is the pathway of protein synthesis?

DNA is copied into mRNA, which travels to a ribosome that builds the protein

What is mRNA's role in making proteins?

it carries the DNA instructions out to the ribosome as a blueprint

Why do different cells take on different roles?

they make different proteins, which is called protein expression

What is the endoplasmic reticulum?

a system of connected membranes inside the cell

What is the rough endoplasmic reticulum?

ER with ribosomes attached that processes proteins

What is the smooth endoplasmic reticulum?

ER without ribosomes that builds lipids and detoxifies drugs and poisons

What is the difference between rough and smooth ER?

rough ER has ribosomes and handles proteins, while smooth ER has none and makes lipids

What is the Golgi body?

a stack of disc-shaped sacs that modify, sort, and package molecules

What are vesicles?

small membrane sacs that bud off and carry substances around and out of the cell

What is the transport pathway of a protein through these organelles?

rough ER, then a vesicle to the Golgi, then a vesicle to its destination

How does a cell's organelle make-up reflect its job?

cells that secrete a lot of protein have plenty of rough ER

What is the mitochondria known as?

the powerhouse of the cell

What process takes place in the mitochondria?

cellular respiration

What is cellular respiration?

the process that releases chemical energy from food molecules to make usable energy for the cell

What do mitochondria produce?

ATP, the cell's usable energy

Where are mitochondria found?

in nearly all eukaryotic cells

What is unusual about mitochondrial DNA?

mitochondria have their own DNA, inherited from the mother

What is the likely origin of mitochondria?

they were once independent cells that came to live inside our ancestors' cells (endosymbiosis)

What are chloroplasts?

the organelles that carry out photosynthesis

What is photosynthesis?

the process that converts sunlight energy into chemical energy stored in sugars

Which cells have chloroplasts?

plant cells and some protists, but not animal cells

What stacks are found inside chloroplasts?

thylakoids

What is the difference between what mitochondria and chloroplasts do?

chloroplasts capture and store energy by photosynthesis, while mitochondria release energy by respiration

How do chloroplasts and mitochondria work together in a plant?

chloroplasts make sugars, and mitochondria then use those sugars to make usable energy

Why do muscle cells have many mitochondria?

to generate enough energy for movement

Why do sunlit leaf cells have many chloroplasts?

they get lots of sunlight, so they do lots of photosynthesis

What is a vacuole?

a storage compartment holding water and enzymes

Why are vacuoles important in plant cells?

they are very large and help give the plant structure

What is a lysosome?

a compartment of enzymes that breaks down waste and foreign substances

What is the difference between a vacuole and a lysosome?

a vacuole mainly stores materials, while a lysosome mainly breaks things down