In an osmosis investigation, potato cylinders are weighed, left in sucrose solutions and then weighed again. Explain why each cylinder is blotted dry before it is reweighed.

Solution clinging to the surface would add to the mass and make the change in mass appear larger than it really is.

Explain why percentage change in mass is used rather than the change in mass in grams.

The cylinders do not all start at exactly the same mass, so using a percentage allows a fair comparison between them.

Explain why a potato cylinder gains mass in pure water.

The cell sap is more concentrated than the surrounding water, so water enters the cells by osmosis.

Edexcel GCSE Combined Science Biology 1SC0

Key Concepts in Biology

Topic overview Eukaryotic and prokaryotic cells Specialised cells and their adaptations Microscopes and magnification calculations Size, scale and units in cell biology Enzyme action and denaturation Factors affecting enzyme activity Enzymes in synthesis and digestion, and rate calculations Diffusion, osmosis and active transport Osmosis in potatoes and percentage change in mass

Cells and Control

Topic overview Mitosis and the cell cycle Why mitosis matters: growth, repair and cancer Growth, differentiation and percentile charts Stem cells and their use in medicine Neurones, receptors and the reflex arc

Genetics

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Natural Selection and Genetic Modification

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Plant Structures and Their Functions

Topic overview Photosynthesis as an endothermic reaction Limiting factors in photosynthesis Light intensity and the rate of photosynthesis Root hair cells, xylem and phloem Transpiration and translocation Factors affecting the rate of transpiration

Animal Coordination, Control and Homeostasis

Topic overview Hormones, endocrine glands and homeostasis The menstrual cycle and its hormones Hormonal and barrier contraception Controlling blood glucose, and type 1 diabetes Type 2 diabetes and body mass

Exchange and Transport in Animals

Topic overview Why multicellular organisms need exchange surfaces Alveoli and gas exchange The blood and its components Arteries, veins and capillaries The heart and the circulatory system Cellular respiration as an exothermic reaction Aerobic and anaerobic respiration compared Investigating the rate of respiration Cardiac output, stroke volume and heart rate

Ecosystems and Material Cycles

Topic overview Levels of organisation and interdependence Abiotic and biotic factors in a community Parasitism and mutualism Sampling with quadrats and transects Estimating population size from field data Human impact on ecosystems and biodiversity The carbon cycle The water and nitrogen cycles

Key Concepts in Biology

Osmosis in potatoes and percentage change in mass

3 things to know
Papers 1 and 2

Overview

Preparing and blotting potato cylinders and the variables in the osmosis investigation, why tissue gains or loses mass, calculating percentage change in mass and final mass, using repeats and means, and writing up an investigation from aim and hypothesis to conclusion and evaluation, and other ways to communicate findings.

What you need to know

Answer each one before you reveal it.

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Key term

Describe how potato cylinders are prepared for an investigation into osmosis.

Key term

Identify the independent and dependent variables in an investigation into osmosis in potatoes.

Key term

Name three variables that must be controlled in an investigation into osmosis in potatoes.

Questions from this subtopic

Each one with the model answer underneath.

1
Describe how potato cylinders are prepared for an investigation into osmosis.
Model answer
Cut cylinders of the same length and diameter with a cork borer, blot them dry and record the mass of each one before it is placed in solution.
2
Identify the independent and dependent variables in an investigation into osmosis in potatoes.
Model answer
The independent variable is the concentration of the sugar solution, and the dependent variable is the percentage change in mass of the potato.
3
Name three variables that must be controlled in an investigation into osmosis in potatoes.
Model answer
The temperature, the time left in the solution, and the starting size of each potato cylinder.
4
In an osmosis investigation, potato cylinders are weighed, left in sucrose solutions and then weighed again. Explain why each cylinder is blotted dry before it is reweighed.
Model answer
Solution clinging to the surface would add to the mass and make the change in mass appear larger than it really is.
5
Explain why percentage change in mass is used rather than the change in mass in grams.
Model answer
The cylinders do not all start at exactly the same mass, so using a percentage allows a fair comparison between them.
6
Explain why a potato cylinder gains mass in pure water.
Model answer
The cell sap is more concentrated than the surrounding water, so water enters the cells by osmosis.

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Key Concepts in Biology

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Natural Selection and Genetic Modification

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