Cell biology

A cell is the smallest unit alive on planet earth

There are two types of cells

  • Prokaryotic (no nucleus)

  • Eukaryotic (nucleus)- bigger than prokaryotic cells

Structure of a eukaryotic cell

  • Nucleus- contains DNA

  • Cytoplasm- chemical reactions take place

  • Cell membrane- controls what comes in and out the cell

  • Mitochondria- respiration

  • Ribosomes- protein synthesis

  • Chloroplasts (made up of chlorophyll)- photosynthesis

  • Rigid cell wall (made of cellulose)- supports and structures the cell

  • Vacuole- contains cell sap

Structure of a eukaryotic cell

  • Cell wall

  • Cell membrane

  • Ribosomes

  • Flagella

  • Circular strand of DNA- genes they need to survive and reproduce & circular chromosome

  • Plasmids (extra genes)

Features of a living organism

  • Movement

  • Respiration

  • Sensitivity

  • Growth

  • Reproduction

  • Excretion

  • Nutrition

Light microscope

  • Easy to use

  • Cheaper than electron microscope

  • Relies on light sources

  • Resolution= 0.2 micrometers - any detail less than 0.2 micrometers will be blurry

  • Used to see individual cells e.g onion cells

  • Not good enough to see sub cellular structures e.g mitochondria

Electron microscope

  • Very expensive

  • Difficult to use

  • Uses electrons

  • Maximum resolution= 0.1 nm (x2000 better than the light microscope

  • Can see sub cellular structures

Magnification is how many times larger the image is than the object

  • Magnification= image size divided by object size

Resolution is the shortest distance between two points on an object that can still be distinguished as two separate elements

Diffusion is the net movement of particles from a high concentration to a low concentration

  • Diffusion happens through partially permeable membranes- only some molecules can diffuse through e.g water, glucose and amino acids

  • Larger molecules can not pass through the partially permeable membrane e.g starch and proteins

  • Passive process- doesn’t require any energy from the cell

Osmosis is the net movement of water molecules across a partially permeable membrane from a high water concentration to a low water concentration (the amount of water, as compared to other molecules, dissolved in the water)

  • Passive process

Active transport is the net movement of particles from a low concentration to a high concentration

  • Moves against the concentration gradient

  • Requires respiration from the cell

Differentiation is the process by which cells change to become specialised. Their journey looks like:

  • Sperm and egg join to make a zygote (fertilised egg cell)

  • Mitosis occurs and cells divide, they become embryonic stem cells

  • Embryonic stem cells differentiate into specialised cells e.g red blood cell

  • After 9 months, a child is born

Stem cells have two key features

  • Divide by mitosis to form more cells

  • Able to differentiate into specialised cells

Humans and plants are made up of many different types of cells, these cells are called specialised cells

  • Specialised cells have a specific role in the body

  • To help them carry out their role, they are shaped in a certain way

  • Specific amounts of different organelles

Examples in plants and humans (there are around 200 different types of specialised cells in humans)

  • Sperm cells- deliver genetic material to an egg in order to fertile it. Adaptations= half as much genetic information as an adult cell, flagellum acts like a tail to swim to reach the egg, streamlined cell, lots of mitochondria, digestive enzymes to break into the egg

  • Muscle cells

  • Nerve cells

  • Root hair cells

  • Phloem cells

  • Xylem cells