Describe the nucleus.
- Central part of the cell.
- Lipid bilayer and DNA.
- Stores genetic information (instructions for making proteins) as DNA in structures called chromosomes (46 in human cells).
- Controls cell growth, division, and functions by regulating protein synthesis.
Describe the cytoplasm.
- Inside the membrane and surrounding every internal organelle.
- Jelly-like, water and molecules floating in it.
- Medium for things to float in and a “cushion”.
- Contains structures like ribosomes and vesicles.
Describe the cell membrane.
- Surrounds the cell.
- Lipid bilayer.
- Protects and contains the cytoplasm and controls the movement of molecules in and out of the cell (selectively permeable).
Describe the cell wall.
- Surrounds the outside of the cell membrane.
- Chitin (fungi), cellulose (plants), or peptidoglycan (bacteria).
- Extra layer of protection for more extreme environments and also helps keep shape (turgor).
- Porous and therefore not a barrier to water or dissolved substances (freely permeable).
Describe mitochondria.
- Floating in the cytoplasm.
- Lipid bilayer.
- Perform cellular respiration, which releases energy from nutrient molecules.
- Cells that require lots of energy, such as muscle and nerve cells, contain many mitochondria.
- Contains a very small amount of DNA, known as mitochondrial DNA.
Describe chloroplasts.
- Found only in cells from the green parts of a plant, like the leaves: cells from parts of a plant that are not green, such as the flowers, roots and woody stems, have no chloroplasts.
- Floating in the cytoplasm.
- Surrounded by lipid bilayer.
- Perform photosynthesis, which creates sugars (like glucose) from carbon dioxide and water using energy from sunlight.
- They are green because of having a green pigment called chlorophyll.
Describe ribosomes.
- Floating in the cytoplasm and on the membranes of some organelles.
- Proteins and nucleic acids (RNA).
- Synthesize proteins from amino acids using instructions from the DNA in the nucleus (translation).
- Cells that produce large quantities of protein, such as pancreatic cells (which make enzymes or insulin), have many ribosomes
Describe vacuoles.
- Center of the cell.
- Lipid bilayer, with a watery liquid storing dissolved sugars, mineral ions, and other solutes (cell sap) inside.
- Fills up so much that it pushes against the cell wall of the plant cell.
- Stores sap (water, nutrients, and waste products). It helps maintain turgidity and support the plant structure.
- Animal cells - small and temporary
Describe vesicles.
- Small bubble-like sacs in the cell.
- Made of lipid bilayer and filled with water and molecules.
- Used to store, transport, or break down substances inside the cell.
What is a plasmid?
Organelle that only appears in prokaryotic cells. It’s a small circular piece of DNA that is separate from the main chromosome.
What are the similarities and differences between plant and animal cells?
Similarities
1. Both eukaryotic
2. Both multicellular
3. Both have nucleus, cell membrane, cytoplasm, mitochondria and ribosomes
4. Both respire, sense, excrete and maintain homeostasis
5. Both can be specialized
Differences
1. Plant cells have cell walls, chloroplasts and big, central and permanent vacuoles.
2. Plant cells move by growing (dividing) in a specific direction (tropisms)
3. Plant cells can reproduce both asexually and sexually, but animal cells can only do it sexually
What is the structure of a bacterial cell?
- Cell wall
- Cell membrane
- Cytoplasm
- Circular DNA
- Ribosomes
- Plasmids
Note:
- No membrane-bound organelles; everything is floating around in the cytoplasm
How are new cells made?
New cells are produced by division of existing cells.
What are the different kinds of specialized cells, and what are their functions?
Animal cell types:
- Stem cells – become a specialized cell by differentiation
- Intestinal cells
- Ciliated cells – movement of mucus in the trachea and bronchi
- Red blood cells – transport of oxygen
- Sperm and egg cells (gametes) – reproduction
Plant cell types:
- Root hair cells – absorption
- Palisade mesophyll cells – photosynthesis
What is a stem cell?
Stem cells are cells that have the ability to divide many times by mitosis while remaining undifferentiated. Later in its life cycle, a stem cell can differentiate into a specialized cell (such as a muscle or nerve cell).
What are the two main types of stem cells?
- Embryonic stem cells are found in the early stages of the development of the embryo.
- Adult stem cells are found in certain adult tissue (such as the bone marrow or the lining of the intestine). They have lost the ability to differentiate into any type of cell but they can form a number of specialized tissues (bone marrow cells can divide many times but can only form different types of red and white blood cells).
What is the importance of cell differentiation in the development of specialized cells?
Differentiation is when certain genes are “switched on” (used as instructions to make proteins) and other genes are “switched off,” causing a stem cell to become a type of specialized cell.
How do multicellular organisms, like plants or animals, grow from a single stem cell to have specialized cells?
- They begin life as a single fertilized egg cell, called a zygote.
- This zygote divides via mitosis.
- Cells become specialized to carry out particular roles depending on where they are located in the embryo.
How can different specialized cells develop even though they have the same genes?
- Genes control the activities in the cell by determining which proteins the cell can make.
- Therefore, for cells to function differently, they must produce different proteins
- So, to make different specialized cells, different genes are “switched on or off” in different cells.
- And which cell is made depends on which genes are “switched on or off”.
What is micropropagation?
Micropropagation is a method of plant propagation using extremely small pieces of plant tissue taken from a carefully chosen and prepared mother plant and growing these under laboratory conditions to produce new plants.
Do plants have stem cells, and what makes them unique?
Plants also contain stem cells but unlike mammals, differentiated plant cells often have the ability to “undifferentiate” and produce stem cells from which they can then make any tissue type. This feature is used when carrying out micropropagation.
What are stem cells used for outside of how the organism works?
They are used for stem cell therapy, which is used to:
1. treat and prevent disease
2. repair damaged tissues
Some examples include:
1. in leukaemia patients where chemotherapy has destroyed healthy cells a bone marrow transplant supplies stem cells that can divide and differentiate to replace these lost cells
2. embryonic stem cells from fertility clinics where parents decide to donate their unused embryos for research could be used to treat many diseases such as diabetes, Parkinson’s disease and even repair damaged nerve tissue (still in the experimental stage)
What are the advantages and disadvantages of using embryonic stem cells?
Advantages of using embryonic stem cells include:
- Embryonic stem cells can make any cell type.
- There are many spare embryos from in vitro fertalisation (IVF) that would otherwise be allowed to perish. Using them for stem cells would mean that they have been used to improve other human lives.
- If cloned embryonic stem cells are produced, they will have identical genes to the patient and so will not be rejected.
Disadvantages of using embryonic stem cells include:
- Using embryonic stem cells raises ethical issues about “killing” potential human lives.
- If spare embryos from in vitro fertalisation are used, they will not be genetically identical to a patient and so could be rejected by the patient’s immune system.
- Human embryos are difficult to grow in culture and are very fragile. This makes cloning inefficient.
- To obtain human eggs and embryos, women need to donate eggs meaning that there may be too few potential donors. Recently, the use of enucleated animal eggs has been proposed to avoid this problem.
- It is difficult to make embryonic stem cells differentiate into the correct cell types. If they do not differentiate properly, they may form tumours and cancers in the body.
What are the advantages and disadvantages of using adult stem cells?
Advantages of using adult stem cells include:
- These cells are easier to control as they are already partly differentiated. They are less likely to cause tumours.
- There are fewer ethical issues than when using embryonic stem cells as no embryos are killed.
- There are no concerns regarding a shortage of embryos or need for donors.
- If a patient’s own cells are used, they will be genetically identical and not rejected by the patient.
Disadvantages of using adult stem cells include:
- Not all cell types can be produced from adult stem cells. Nerve cells are very difficult to produce from adult stem cells making it difficult to create therapies for spinal cord and brain repair.
- Adult stem cells can be difficult to extract.
- Cells can age so adult stem cells taken from older people may not last long.
