Command Terms in IB Biology------中


Command Terms in IB Biology

All IB Biology questions and assessment statements are built around  these

command terms, which let you know exactly what is expected of  you.


"Add brief notes to a diagram or graph."


Annotate a graph showing hormone levels in the menstrual cycle.” 


• Annotate is more than just ‘label’ – some causes or explanation must be given

• Make up a gallery of annotated graphs, diagrams, flow-charts etc, and use them as visual organisers in your revision of complex concepts


"Use an idea, principle, theory, law or equation in a new situation." 


Apply the dichotomous key to identify ribosomes.” 


• Put an idea or technique into action

• Make up some of your own dichotomous keys, for any topic or process

• Learn the equations needed, as they too might need to be ‘applied’


"Find a numerical answer, showing the relevant stages of working." 


Calculate the percentage difference in .”response time of the control group from day 2 to day 31

-increases from 130s to 145s - 145-130 = 15s

-Percentage difference = of the original measurement?

So: % diff  =   (15/130) x 100                  

                  =  11.5%


• Learn all the different ‘calculate percentage…’ methods. 

• Make sure you use the correct SI unit in your answer

• Make up a booklet of all the possible types of calculations you have learned to use


"Give a detailed account." 


Describe the effect of previous exposure to the odor on the flight of bees.” (2)

Experimental group fly more around odor source;

Greater circling in experimental group;

Experimental group fly more directly to odor source;

More oriented flight in experimental group.

Describe how biomass may be measured.” (2)

Organism is cleaned of dirt or soil;

Mass is recorded;

Organism is dried in an oven until constant mass reached;

Biomass is total dry mass.  


• Descriptions are not explanations

• Pay attention to the number of marks available

• Descriptions can be of processes or of parts of a data response graph 


"Give the differences between two or more different items."


Distinguish between autotroph and heterotroph.”

Autotroph: organism that synthesises its organic molecules from simple inorganic substances. 

Heterotroph: organism that obtains organic molecules from other organisms. 


• Looking for as many differences as there are marks awarded

• No need to present similarities

• Build a chart, with all possible compare/ distinguish questions you can think of


"Find an approximate value for an unknown quantity." 


Describe one technique used to estimate population size of an animal species, based on capture-mark-recapture methods.”

 Capture (humanely) a sample of the population;

Control for time and area; 

Example of capture method;

Count and apply mark (non-harmful) to organism;

Release back to habitat; Second capture takes place;

Count all individuals with and without marks;

Apply Lincoln Index to estimate population size;

n1 =  first capture, n2 = total in second capture, n3 = recapture with marks. 


• Estimations may come from graphical questions

• Estimation techniques are used in ecology , rather than direct measurement

• Make a note of all instances of ‘estimate’ in the subject guide


“Give a brief account or summary."


Outline the light dependent reactions of photosynthesis (HL, 6 marks).”

Light energy is absorbed by photosystem II;

Electrons excited/ photoactivated by absorption of light energy;

Electron passed along a series of carriers;

NADP+ reduced to NADPH + H+;

Photolysis of water produces oxygen and hydrogen; 

Called non-cyclic photophosphorylation;

H+ pumped across thylakoid membrane, through ATP synthase  (by chemiosmosis), generating ATP.  


• Pay close attention to the number of marks available

• Present answers clearly to get the complete number of marks

• Outline is a summary or account, without reasons or explanation (step-by-step) 


"Find an answer from a given number of possibilities." 


Identify the response time of group 2 on day 31 of the study.”

 183 seconds (unit needed)

Identify the group with the largest difference in response time from day 2 to day 31.”


• Identify – pick one single answer

• Practice making your own ‘identify’ questions using different types of graphs

• Identify can also be used for parts of diagrams, such as curves, organelles etc.