S1 - The nature and Variety of Organisms

Question 1

What are the characteristics of living organisms:

Answer 1

M ovement
R espiration
S ensitivity
C ontrol
G rowth
R eproduction
E xcretion
N utrition

Question 2

What deos a typical animal cell contain?

Answer 2

-nucleus: an organelle which contains the genetic material that controls the cell’s activities, it is surrounded by its own membrane
-cell membrane: this membrane forms the outer surface of the cell and controls the substances that go in and out
-cytoplasm: a gel-like substance where most of the cell’s chemical reactions happen, it contains enzymes which control these reactions
-mitochondria: small organelles where most of the reactions for aerobic respiration take place
-ribosomes: small organelles where proteins are made in the cell

Question 3

What does a typical plant cell contain?

Answer 3

-chloroplasts: photosynthesis, which makes food for the plant happens here, they contain a green substance called chlorophyll, which is used in photosynthesis
-cell wall: a rigid structure made of cellulose, which surrounds the cell membrane, it supports the cells and strengthens it
-vacuole: a large organelle that contains cell sap which helps to support the cell

Question 4

What are tissues?

Answer 4

-a tissue is a group of similar cells that work together to carry out a particular function
-a tissue can contain more than one cell type

Question 5

What are organs? What do they do?

Answer 5

-an organ is a group of different tissues that work together to perfom a function
-lungs in mammals and leaves on plants are examples of organs-they’re both made up of several different tissue types

Question 6

What are organ systems and what do they do?

Answer 6

-organs work together to form organ systems, each system does a different job
-for example, in mammals, the digestive system is made up of organs including the stomach, intestines, pancreas and liver
organelle -> cell -> tissue -> organ -> organ system

Question 7

About Eukaryotic organisms:

Answer 7

-organisms that have a nucleus and organelles that are found within a plasma membrane
-plants
-animals
-fungi

Question 8

About Plants:

Answer 8

e.g: cereals (maize) and herbaceous legumes (peas)
-plants are multicellular
-they have chloroplasts which means they can photosynthesise
-they have cell walls, which are made of cellulose
-plants store carbohydrates as sucrose or starch

Question 9

About Animals:

Answer 9

e.g: mammals (humans) and insects (flies)
-animals are multicellular
-they don’t have chloroplast so they can’t photosynthesise
-don’t have cell walls
-most have nervous coordination
-animals store carbohydrates as glycogen

Question 10

About Fungi:

Answer 10

e.g: yeast (single-cell) or mucor (multicellular)
-some are single-celled
-others have a body called mycelium made up of hyphae (thread-like structures) containing lots of nuclei
-can’t photosynthesise
-have cell walls made of chitin
-most feed by saprotrophic nutrition
-fungi store carbohydrates as glycogen

Question 11

About Prokaryotic cells:

Answer 11

-do not have a nucleus or membrane-bound organelles
-protoctists
-bacteria
-viruses

Question 12

What are protoctists? What do they do?

Answer 12

e.g: chlorella (plant-cell-like) or amoeba (animal-cell-like)-live in pond water
-these are single-celled and microscopic
-some have chloroplasts and are similar to plant cells
-other are more like animal cells

Question 13

What are bacteria? What do they do?

Answer 13

e.g: lactobacillus bulgaricus (used to make yoghurt) or pneumococcus (causes pneumonia)
-single-celled and microscopic
-don’t have a nucleus
-they have circular chromosome of DNA
-some can photosynthesise
-most bacteria feed off other organisms (dead or alive)

Question 14

What are viruses? What do they do?

Answer 14

e.g: influenza virus (prevents chloroplast formation), tobacco mosaic virus or HIV which lead AIDS
-viruses are small particles -not living organisms
-parsitics: can only reproduce within living cells, can infect every type of organisms
-they come in loads of different shapes and sizes
-do not have a cellular structure-they have a protein coat around some genetic material (either DNA or RNA)

Question 15

What are pathogens? What do they do?

Answer 15

-are disease-causing organisms that include some fungi, protoctists and bacterias
-protoctist: plasmodium, which causes malaria
-bacterium: pneumococcus, which causes pneumonia
-viruses: influenza virus (which cause ‘flu’) and HIV (which causes AIDS)

Question 16

What are enzymes? What do they do?

Answer 16

-they are protein molecules and the shape of the enzyme is vital to its function
-this is because each enzyme has its unqiely shaped active site where the substrate binds
-a simplified way to look at it is the Lock and Key Hypothesis:
-the shape of the substrate is complementary to the shape of the active site (enzymes specificity), so when they bond it forms an enzyme-substrate complex
-once bound, the reaction takes place and the products are released from the surface of the enzyme

Question 17

How does temperature affect enzymes functions?

Answer 17

-the optimum is around 37ºC (body temperature)
-the rate of reaction increases with an increase in temperature up to this optimum, but above this temperature it rapidly decreases and eventually the reaction stops
-when the temperature becomes too hot, the bonds in the structure will break
-this changes the shape of the active site, so the substrate can no longer fit in, which means it is denatured

Question 18

Practical: Investigate how enzyme activity can be affected by changes in temperature.

Answer 18

1) Starch solution is heated to set temperature
2) Amylase is added
3) Iodine is added to each well after a minute
4) Measure the time it takes until the iodine stops turning blue-black (meaning starch is present)
5) Repeat the test with different temperature

Question 19

How does pH affect enzyme functions?

Answer 19

-the optimum pH for most enzymes is 7, but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH
-if the pH is too high or too low, the forces that hold the amino acids chains that make up the protein will be affected
-this will change the shape of the active site, so the substrate can no longer fit in
-the enzyme is said to be denatured and can no longer work

Question 20

What is diffusion:

Answer 20

-diffusion is the spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration
-it is a passive process as no energy is required
-the molecules have to be small in order to be able to move accross, for example oxygen, glucose, amino acids and water, but larger molecules such as starch and proteins cannot

Question 21

What is osmosis?

Answer 21

-> the movement of water from a less concentrated solution to a more concentrated one through a partially permeable membrane
-a dilute solution of sugar has a high
concentration of water (high water potential) and vv
-water moves from a dilute solution to a concentrated solution because it moves from ana area with high water potential to low water potential- down a concentration gradient
-it is a passive process

Question 22

Practical: Investigating osmosis in potatoes.

Answer 22

1) place different sucrose solutions including 0% for a control, in different boiling tubes
2) dry potato strips on a paper towel and measure the masses
3) place each potato strip into each sucrose solution for 20 mins and record how the mass changed
4) repeat tests at each solution several times with potato strips of similar masses

Question 23

Practical: investigate diffusion in non-living systems.

Answer 23

1) cut a 1cm^3 cube of agar made of sodium hydroxide and phenolphthalein
2) place cube in solution with hydrochloric acid
3) remove the cube and wash with water to stop further reaction
4) cut the cube in half and measure the distance that the acid has caused agar to become colourless from outside inwards
5) repeat the experiment two more times and calculate the mean
6) repeat with different concentrations of hydrochloric acid

Question 24

Why do unicellular organisms rely on diffusion for the movement of substances?

Answer 24

-in small single-celled organisms can use diffusion to transport molecules into their body from the air-this is because they have a relatively large volume surface : volume ratio
-due to their low metabolic demands, diffusion accross the surface of the organism is sufficient enough to meet its needs

Question 25

The need for a transport system in multicellular organisms:

Answer 25

-multicellular organisms have a small surface area : volume ratio so they cannot rely on diffusion alone
-instead, surfaces and organ systems have a number of adaptations that allows molecules to be transported in and out of cells, examples (alveoli in the lungs, villi in the small intestines and root hair cells in plants)