aqa gcse biology triple science topic 1

What are eukaryotic cells?

Cells that are more complex and have a nucleus (animal and plant cells)

What are prokaryotic cells?

Cells that are smaller and simpler, and don't have a nucleus but still have genetic information (bacteria)

What are eukaryotes?

Organisms made of eukaryotic cells

What is a prokaryote?

A prokaryotic cell (it's a single celled organism)

What is cytoplasm?

A liquid gel in which most of the chemical reactions needed for life take place. It contains enzymes that control these chemical reactions

In what types of cells is cytoplasm found?

Animal, plant, algae, and bacteria cells

What is the cell membrane?

It holds the cell together and controls the passage of substances in and out of the cell

In what types of cells is a cell membrane found?

Animal, plant, algae, and bacteria cells

What is the nucleus?

It carries the instructions for making new cells or organisms and controls all activities of the cell

In what types of cell is a nucleus found?

Animal, plant, and algae cells

What is the cell wall?

It is made of cellulose in plants and peptidoglycan in bacteria. It strengthens and supports the cell.

In what types of cell is a cell wall found?

Plant, and bacteria cells

What are chloroplasts?

They are found in the green parts of a plant, and they contain chlorophyll which allows the cell to create food and light energy

In what types of cell are chloroplasts found?

Plant, and algae cells

What are ribosomes?

They are the site of protein synthesis. All the proteins needed in the cell are made here. The ribosomes are attached to the RER (rough endoplasmic reticulum)

In what types of cell are ribosomes found?

Animal, and plant cells

What are mitochondria?

They are structures in the cytoplasm. Oxygen is used, and energy is released during respiration here

In what types of cell are mitochondria found?

Animal, plant, and algae cells

What is a permanent vacuole?

It is a space in the cytoplasm filled with cell sap. It is important for keeping the cell rigid to support the plant

In what types of cell is a permanent vacuole found?

Plant, and algae cells

What is a plasmid?

A small, circular piece of DNA that carries genes additional to those in the main genetic material

What two features do bacteria cells NOT have?

Chloroplasts and mitochondria

How do light microscopes work?

They use light and lenses to form an image of a specimen and magnify it

What can we see using a microscope?

Individual cells and large sub-cellular structures, like nuclei

What do electron microscopes use to form an image?

Electrons

Out of electron and light microscopes, which has a higher resolution?

Electron microscopes

What can we see with electron microscopes?

The internal structure of mitochondria and chloroplasts, ribosomes, and plasmids

What is the formula for magnification?

Magnification is image size divided by real size

How do you convert from micrometres into millimetres?

Divide by 1000

What is a flagellum for?

Locomotion

In what type of cell is a flagellum found?

Bacteria

What are nerve cells specialised to do?

Carry impulses around an organism. They provide a quick communication system

What are four adaptations of nerve cells?

Lots of dendrites to connect with other cells

Axon that carries nerve impulses from one place to another

Synapses adapted to pass impulses on using transmitter chemicals

Long so they cover more distance

What is differentiation?

The process where a cell changes to become specialised

What are stem cells?

Undifferentiated cells

What are sperm cells specialised to do?

Get the male DNA to the female DNA by fertilising an egg

What are three adaptations of sperm cells?

Long tail to help it swim

Lots of mitochondria to provide the energy needed for the sperm cell to move

Digestive enzymes in the head to digest the egg cell membrane

What are muscle cells specialised to do?

Contract and relax to move the bones of the skeleton

What are two adaptations of muscle cells?

Long so they have space to contract

Contain lots of mitochondria to generate the energy needed for contraction

What are root hair cells specialised to do?

Absorb water and minerals

What is one adaptation of a root hair cell?

Large surface area for absorbing water and mineral ions from the soil

What are photosynthetic cells specialised to do?

Carry out photosynthesis

What are three adaptations of photosynthetic cells?

Contain chloroplasts, which contain chlorophyll for photosynthesis

Positioned in continuous layers in the leaves and outer layers of the stem of a plant to help absorb light

Have a large permanent vacuole to keep the cell rigid

What are xylem cells specialised to do?

Carry water and mineral ions from the roots to the highest leaves and shoots

What are two adaptations of xylem cells?

Xylem cells are alive when they are first formed, but die and form hollow tubes for the water and mineral ions to pass through

They have rings of lignin to help withstand the pressure of water in the plant

What are phloem cells specialised to do?

Carry food around the plant (translocation)

What are two adaptations of phloem cells?

The cell walls between the cells break down and form sieve plates which allow water and dissolved food to move as needed.

They are supported by the companion cells that transfer the energy needed to move the food.

Where are stem cells found in adults?

Bone marrow

What is the difference between embryonic stem cells and adult stem cells?

Adult stem cells can only turn into certain cell types, like blood cells, whereas embryonic stem cells can turn into any type of cells

How can adult stem cells be used to cure disease?

Stem cells transferred from the bone marrow of a healthy person can replace faulty blood cells in the patient who receives them

How can embryonic stem cells be used?

Make insulin-producing cells for diabetics

Nerve cells for people paralysed by spinal injuries

What is therapeutic cloning?

The embryo could be made to have the same genetic information as the patient, meaning the stem cells produced wouldn't be rejected by the patient's body as the genes are the same.

What is a risk of using stem cells in medicine?

Stem cells may get contaminated with a virus, which could be passed on to the patient, making them sicker

Give one argument against using stem cell research

Each one is a potential human life

Give one argument for using stem cell research

Curing patients who are suffering is more important than the rights of embryos

How can stem cells be used for plants?

Produce clones quickly and cheaply

Grow more plants of rare species

Grow crops that have desired features (e.g. disease resistance)

What are chromosomes?

Coiled up lengths of DNA molecules

How many copies of each chromosome does a body cell normally have?

Two - one from each parent

How many pairs of chromosomes does a human cell have?

23

What is mitosis?

Division of cells

What do multicellular organisms use mitosis for?

Growth, or to replace cells that have been damaged

What do cells do before they divide?

Increase their sub-cellular structures, like mitochondria and ribosomes

Duplicates its DNA. The DNA is copied and forms X-shaped chromosomes - the left arm of the chromosome has the same DNA as the right arm

Describe the process of mitosis

The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell. Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells. Lastly, the cytoplasm and cell membrane divide. The cell has now produced two new daughter cells, which contain the same DNA as the parent cell.

What is the name of the process where prokaryotic cells reproduce?

Binary fission

Describe the process of binary fission

The circular DNA and plasmid(s) replicate. The cell gets bigger and the circular DNA strands move to opposite 'poles' of the cell. The cytoplasm begins to divide and new cell walls begin to form. The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s).

How do you calculate the number of bacteria in a population?

2 to the power of (Time allowed for reproduction divided by mean division time)

What does a culture medium contain?

Carbohydrates, minerals, proteins, and vitamins

What are the wire loops used to transfer micro-organisms called?

Inoculating loops

Why are cultures of micro-organisms not kept above 25 degrees at schools?

Harmful pathogens are more likely to grow above this temperature

How do you avoid contamination of cultures?

Sterilise the Petri dishes and culture medium

Sterilise the inoculating loop before using by passing it through a flame

Tape the lid of the Petri dish lightly to stop micro-organisms from the air getting in

Store the Petri dish upside down as it prevents condensation from falling onto the agar surface

What is the inhibition zone?

The area in a Petri dish where bacteria cannot grow

How do you calculate the inhibition zone?

Area = Pi x (radius)^2

What should you soak the paper disk in as a control?

Sterile water

What is diffusion?

Diffusion is the spreading out of particles from an area of higher concentration to an area of lower concentration

In what states does diffusion happen?

Liquid solutions, and gases

What happens to the rate of diffusion when the concentration gradient is large?

Diffusion is faster

How does temperature affect the rate of diffusion?

The higher the temperature, the faster the rate of diffusion. This is because the particles have more energy so they move around faster

Give four substances that diffuse through cell walls

Oxygen, glucose, amino acids, and water

How does surface area affect the rate of diffusion?

The larger the surface area, the faster the diffusion rate. This is because more particles can pass through at once

What is osmosis?

Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to an area of lower concentration

Why can't root hair cells use diffusion to take in minerals?

The concentration of minerals is usually a lot higher in the root hair cell than in the soil

How do root hair cells take in minerals?

Active transport. This process allows the plant to absorb minerals against a concentration gradient, which is essential for growth.

What does active transport need?

Active transport needs energy from respiration to work