Osmosis is the movement of water molecules across a partially permeable membrane, from a region of higher concentration of water to a lower concentration of water.
Active Transport in Cell Biology
Active transport is the movement of molecules across a cell membrane against the concentration gradient (from a low concentration to a high concentration). It requires energy from the cell. An example of where active transport is used is in plants, root hair cells absorb water and mineral ions, they have a large surface area for absorption. The minerals that plants need like magnesium ions and nitrates are at a higher concentration inside the cell than in the soil, which means that they can't absorb them via diffusion, instead they have to use energy to absorb them via active transport against their concentration gradient. The energy comes from respiration which happens in mitochondria. Root hair cells are adapted for this by having lots of mitochondria.
Cell Biology - Animal and Plant Cells
Animal Cells
- Eukaryotic cells
- Cell membrane- allows substances in and out of the cell, it is partially permeable to allow osmosis to happen, it is also the site of diffusion
- Ribosome-the site of protein synthesis
- Mitochondria-site of aerobic respiration and provides energy
- Cytoplasm controls the reactions of the cell
- Nucleus contains the DNA and controls the cell
Plant Cells
- Eukaryotic cells
- Cell wall - contains cellulose and provides structure to the cell
- Mitochondria - site of aerobic respiration and provides energy
- Nucleus contains DNA and controls the cell
- Chloroplast- site of photosynthesis and contains chlorophyll which makes the plant green
- Ribosome-site of protein synthesis
- Vacuole contains cell sap, waste products end up here
- Cell membrane allows substances in and out of the cell, it is partially permeable to allow osmosis to happen, it is also the site of diffusion
- Cytoplasm controls the reactions of the cell
Eukaryotes and Prokaryotes in Cell Biology
Animal and plant cells are both examples of eukaryotic cells, they are more complex structures. However, prokaryotes are much smaller and simpler structures e.g. bacteria cells.
Magnification and Microscopes
Magnification
- Magnification = image size / actual size
- x100 x10 x1000 x1000
- cm mm um nm
- /100 /10 /1000/1000
- m
Microscopes
- Object-the real object or sample that you are looking at
- Image - the image that we see when we look down the microscope
- Magnification - how many times larger the image is than the object
- Resolution - the shortest distance between the 2 points on an object which can still be distinguished as 2 separate entities a measure of how detailed the image is
Light Microscopes and Electron Microscopes
Light microscopes:
- easy to use
- relatively cheap
- rely on light
- limited to a low resolution
Electron microscopes:
- harder to use
- very expensive
- use, electrons instead of light maximum resolution is 2000x better than light microscopes
Differentiation and Specialised Cells
Differentiation is the process by which a cell changes to become specialised. In humans, it starts with one cell called zygote (fertilised egg cell), this then cell then divides by mitosis into 2 cells, these 2 cells then divide into 2 more cells each. At this point, none of these cells are specialised yet, they are called stem cells.
Specialised Cells
In animal cells, examples of specialised cells would be sperm cells, muscle cells and nerve cells. In plant cells examples would be root hair cells, phloem cells and xylem cells. Specialised cells have a specific role in the body, to help them fulfil that role they have a specific shape or structure, they also have specific amounts of different organelles. Sperm cells have a long tail to help it swim to the egg, they also have lots of mitochondria for energy to swim. Muscle cells have lots of mitochondria for contraction. Nerve cells are a long and thin to reach far, have they have branched endings to join to other nerve cells. Egg cells have an outer layer which only allows one sperm to penetrate it, they also yolk contain for developing cells.
Stem Cells
In humans, stem cells divide by mitosis which are then able to differentiate into specialised cells. For example, when a sperm cell fertilises an egg cell it forms a single cell called a zygote. This zygote then divides by mitosis to form a small group of cells called an embryo, these are called embryonic stem cells which can differentiate into any type of cell e.g. nerve cells, skin cell or blood cell. After 9 months, these cells develop into a baby. In plants, stem cells are found in plant tissue called meristems, which then differentiate over time into cells such as root hair cells, palisade cells, phloem cells and xylem cells.
Diffusion
Diffusion is the net movement o particles from an area of higher concentration to an area of lower concentration. It can happen in both gases and liquids. Cell membranes are adapted to be partially permeable to allow some molecules through via diffusion. There are 3 factors that affect the rate of diffusion; the size of the molecule, the temperature and the concentration gradient.
