Supplying the Cell (OCR GCSE Combined Science A (Gateway): Biology): Flashcards
Exam code: J250
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Define diffusion.
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Define diffusion.
The net movement of particles from an area of higher concentration to an area of lower concentration.
Define osmosis.
The net movement of water molecules across a partially permeable membrane, from a higher to a lower water concentration.
Why are diffusion and osmosis described as passive?
They need no energy from the cell — particles move using their own kinetic energy.
Name two substances that move into or out of cells by diffusion.
Oxygen and carbon dioxide, which diffuse across the cell membrane during gas exchange.
How does temperature affect the rate of diffusion?
A higher temperature gives particles more kinetic energy, so they move faster and diffusion is quicker.
What does it mean that the cell membrane is partially permeable?
Some substances can pass through it and others cannot.
Small molecules such as oxygen pass through; large molecules such as starch cannot.
Define water potential.
How likely water molecules are to move out of a solution.
Pure water has the highest water potential; a concentrated solution has a low water potential.
In which direction does water move by osmosis?
From a region of high water potential (dilute) to a region of low water potential (concentrated).
A concentrated sugar solution has a ＿＿＿＿＿＿＿＿ water potential than pure water.
A concentrated sugar solution has a lower water potential than pure water.
What happens to an animal cell placed in distilled water?
It gains water by osmosis.
With no cell wall to resist the pressure, the membrane stretches until the cell bursts.
What happens to an animal cell in a concentrated sugar solution?
It loses water by osmosis and becomes shrivelled (crenated).
What happens to a plant cell placed in distilled water?
It gains water by osmosis and the vacuole swells, pushing the membrane against the cell wall.
The cell becomes turgid.
What happens to a plant cell in a concentrated sugar solution?
It loses water by osmosis, the vacuole shrinks and the membrane pulls away from the cell wall.
The cell becomes flaccid.
Why does turgor matter to a plant?
Turgid cells make the plant rigid and firm, holding it upright with its leaves out to catch light.
Without enough water the plant wilts.
Unlike animal cells, plant cells do not burst in pure water because they have a ＿＿＿＿＿＿＿＿.
Unlike animal cells, plant cells do not burst in pure water because they have a cell wall.
True or False?
Osmosis moves any dissolved substance across a membrane.
False.
Osmosis applies only to water. Other substances move by diffusion or active transport.
True or False?
Diffusion needs energy from respiration.
False.
Diffusion is passive. Only active transport needs energy from respiration.
Define active transport.
The movement of substances against a concentration gradient, using energy from respiration.
In which direction does active transport move substances?
From a more dilute solution to a more concentrated one — up the concentration gradient.
Where does the energy for active transport come from?
ATP, released by cellular respiration.
Give the main difference between diffusion and active transport.
Diffusion is passive and moves substances down a concentration gradient.
Active transport needs energy and moves substances against the gradient.
Which plant cells take up mineral ions by active transport?
Root hair cells, on the surface of the roots.
Why must a root hair cell use active transport to take up minerals?
Minerals are more concentrated inside the cell than in the soil water, so they cannot move in by diffusion.
Why do plants need magnesium ions?
To make chlorophyll, the pigment needed for photosynthesis.
Why do plants need nitrate ions?
To make amino acids, which are used to build the proteins needed for growth.
Active transport moves substances ＿＿＿＿＿＿＿＿ the concentration gradient.
Active transport moves substances against the concentration gradient.
Unlike diffusion and osmosis, active transport requires ＿＿＿＿＿＿＿＿ from respiration.
Unlike diffusion and osmosis, active transport requires energy from respiration.
Why would a cell with few mitochondria carry out little active transport?
Mitochondria supply the ATP from respiration that active transport depends on.
Name the three processes that move substances across cell membranes.
Diffusion, osmosis and active transport.
True or False?
Active transport can move substances up a concentration gradient.
True.
That is what distinguishes it from diffusion and osmosis, and why it needs energy.
True or False?
A dead root hair cell could still absorb minerals actively.
False.
A dead cell cannot respire, so there is no ATP to power active transport.
Define the cell cycle.
The series of stages a cell goes through from being formed to dividing to make new cells.
List the stages of the cell cycle in order.
Cell growth
DNA replication
More cell growth
Movement of the chromosomes, then division of the cell
Why must DNA be copied before a cell divides?
So that each new cell receives a complete copy of every chromosome.
Define mitosis.
The type of cell division that produces two genetically identical daughter cells.
Why is mitosis important to an organism?
It allows the organism to grow and to repair damaged tissue.
What happens to the chromosomes during mitosis?
The duplicated chromosomes line up in the centre of the cell.
Cell fibres then pull one copy of each to opposite ends of the cell.
Define cytokinesis.
The stage in which the cytoplasm and cell membrane divide, producing two separate daughter cells.
How many daughter cells does one round of mitosis produce?
Two, and they are genetically identical to each other and to the parent cell.
The two cells produced by mitosis are genetically ＿＿＿＿＿＿＿＿ to each other.
The two cells produced by mitosis are genetically identical to each other.
Before the chromosomes move apart, the cell must copy its ＿＿＿＿＿＿＿＿.
Before the chromosomes move apart, the cell must copy its DNA.
What forms around each group of chromosomes at the end of mitosis?
A new nucleus.
Which body cells are not produced by mitosis?
The gametes (sex cells).
What pulls the duplicated chromosomes apart in mitosis?
Cell fibres, which attach to the chromosomes and pull them to opposite ends of the cell.
True or False?
Mitosis produces cells with half the number of chromosomes.
False.
Mitosis produces cells with the same number of chromosomes as the parent cell.
True or False?
Most of the cell cycle is spent growing and copying DNA.
True.
The growth and DNA replication stages take up far more of the cycle than the division itself.
Define differentiation.
The process by which an unspecialised cell develops a structure suited to a particular job.
Define specialised cell.
A cell with a particular structure and set of sub-cellular structures that suit it to a specific function.
Why is cell differentiation important to an organism?
It produces specialised cells, each doing a particular job well, which lets the organism work far more efficiently.
When do most animal cells differentiate?
At an early stage of development, after which they lose the ability to differentiate.
How do plant cells differ from animal cells in differentiation?
Most plant cells keep the ability to differentiate throughout the plant's life.
How is a red blood cell adapted to its function?
It is biconcave, giving a large surface area for gas exchange, and has no nucleus, leaving more room for haemoglobin.
How is a nerve cell adapted to its function?
It is long, carrying impulses over large distances, with branched endings to connect to other cells.
How is a sperm cell adapted to its function?
It has a tail so it can swim to the egg cell.
How is an egg cell adapted to its function?
It contains a lot of cytoplasm rich in nutrients to supply the developing embryo.
How is a ciliated epithelial cell adapted to its function?
Its hair-like cilia beat to sweep mucus and trapped particles along.
How is a root hair cell adapted to its function?
Its long extension gives a large surface area for absorbing water and mineral ions.
How is a palisade mesophyll cell adapted to its function?
It is packed with chloroplasts, maximising the amount of photosynthesis it can carry out.
How is a xylem cell adapted to its function?
Its top and bottom walls break down to form a continuous hollow tube for water to move through.
＿＿＿＿＿＿＿＿ is the process by which a cell becomes specialised for a particular job.
Differentiation is the process by which a cell becomes specialised for a particular job.
To become a nerve cell, the cytoplasm and membrane of a cell must ＿＿＿＿＿＿＿＿.
To become a nerve cell, the cytoplasm and membrane of a cell must elongate.
True or False?
Most animal cells can differentiate throughout their lives.
False.
Most animal cells differentiate early and then lose the ability. It is plant cells that keep it.
Define stem cell.
An undifferentiated cell that can divide to produce more cells of the same type, or differentiate into other cell types.
Where are stem cells found in animals?
In early embryos, and in certain tissues of the adult such as bone marrow.
Where are stem cells found in plants?
In meristem tissue, in growing regions such as the root and shoot tips.
What is the function of stem cells?
They divide to produce a range of different cell types.
Those cells are used for development, growth and repair.
Define meristem.
Plant tissue containing unspecialised cells that can differentiate into any type of plant cell.
Give an example of a cell that meristem tissue can produce.
A root hair cell, produced by meristem cells in the root.
For how long do plant stem cells keep the ability to differentiate?
Throughout the whole life of the plant.
How are plant stem cells useful to growers?
They can be used to clone plants with a desired characteristic, such as disease resistance.
How does an embryo develop into a complex organism?
Its embryonic stem cells divide and differentiate into all the specialised cell types the organism needs.
What are adult stem cells mainly used for in the body?
Maintaining and repairing tissues, such as replacing damaged blood and skin cells.
A stem cell is described as ＿＿＿＿＿＿＿＿ because it has not yet become a particular type of cell.
A stem cell is described as undifferentiated because it has not yet become a particular type of cell.
Plant stem cells are found in ＿＿＿＿＿＿＿＿ tissue at the root and shoot tips.
Plant stem cells are found in meristem tissue at the root and shoot tips.
True or False?
Stem cells are found only in embryos.
False.
They are found in embryos, in adult animals (such as in bone marrow), and in plant meristems.
True or False?
A stem cell can divide to make more stem cells.
True.
It can produce more undifferentiated cells of the same type, as well as differentiating into other types.
Define embryonic stem cell.
A stem cell found in an early embryo, able to differentiate into any type of cell.
Define adult stem cell.
A stem cell found in certain tissues of an adult, able to differentiate into only a few types of cell.
Give the main difference between embryonic and adult stem cells.
Embryonic stem cells can become any cell type.
Adult stem cells can become only a limited range of cell types.
Where in the body are adult stem cells found?
In particular tissues only, such as the bone marrow.
Where do embryonic stem cells come from?
From an early embryo, where they will go on to form every tissue of the body.
Which cell types do adult stem cells mainly produce?
Mostly blood cells, along with other cells needed to repair the tissue they sit in.
Which type of stem cell is the more versatile, and why?
Embryonic stem cells, because they can differentiate into every cell type rather than just a few.
What job do adult stem cells do in the body?
They maintain and repair tissues by replacing cells that are damaged or worn out.
Are adult stem cells differentiated?
No. Like all stem cells they are undifferentiated — they simply have a narrower range of cells they can become.
＿＿＿＿＿＿＿＿ stem cells can differentiate into any type of cell in the body.
Embryonic stem cells can differentiate into any type of cell in the body.
Adult stem cells can differentiate into only a ＿＿＿＿＿＿＿＿ number of cell types.
Adult stem cells can differentiate into only a limited number of cell types.
Why can an embryo form a whole organism but an adult cannot?
Its stem cells are unrestricted — they can still become every cell type, while adult stem cells are limited to a few.
True or False?
Adult stem cells can become any cell type in the body.
False.
Only embryonic stem cells can. Adult stem cells are limited to a few types.
True or False?
Adults have no stem cells at all.
False.
Adults keep stem cells in certain tissues, such as bone marrow, for repair and replacement.
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