Biology

Question 1

Define Cells

Answer 1

The smallest units from which all organisms are made

Question 2

What is Cell membrane?

Answer 2

A very thing layer surrounding the cytoplasm of every cell; it controls what enters and leaves the cell

Question 3

Define Cell wall

Answer 3

A tough layer outside the cell membrane found in the cells of plants, fungi and bacteria

Question 4

Define Cytoplasm

Answer 4

A jelly like material that fills the cell

Question 5

What is vacoule

Answer 5

A fluid filled space inside a cell, seperated from the cytoplasm by a membrane

Question 6

What is Chloroplast

Answer 6

Small Strucutres found inside some plant cells, inside which photosynthesis takes place

Question 7

Define mithochondrion

Answer 7

Small structure in a cell, where aerobic respiration releases energy for glucose

Question 8

Define aerobic respiration

Answer 8

Chemical reactions that take place inside a cell which uses oxygen to break down glucse and other nutrient molecules to release energy for the cell to use

Question 9

What is ribosomes

Answer 9

very small strucuture in a cell that use information on DNA to make protein molecules

Question 10

What is tissue

Answer 10

A group of cells that work together to perform particular function

Question 11

Define plasmids

Answer 11

A small circular molecules of DNA found in many prokaryotic cells in addition to the main , much larger circles of DNA

Question 12

Define organ

Answer 12

A group of tissues that work together to perform a particular function

Question 13

Define diffusion

Answer 13

The net movement of particles from a region of their higher concentration to a region of lower concentration( down their concentration gradient) as a result of their random movement

Question 14

Define osmosis

Answer 14

The net movement of water molecules from a region of higher water potential ( dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane

Question 15

Define Active transport

Answer 15

The net movement of molecules or ions through a cell membrane from a region of lower concentration to a region of higher concentration ( against the concentration gradient ) using energy for respiration

Question 16

How does active transport works

Answer 16

Active transport works by using carrier proteins embedded in the cell membrane to pick up specific molecules and take them through the cell membrane against their concentration gradient:
-Substance combines with carrier protein molecule in the cell membrane
-Carrier transports substances across membrane using energy from respiration to give them the kinetic energy needed to change shape and move the substance through the cell membrane
-Substance released into cell

Question 17

How does plants obtain food

Answer 17

Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water
At the same time oxygen is made and released as a waste product
The reaction requires energy which is obtained by the pigment chlorophyll trapping light from the Sun

Question 18

Define Photosynthesis

Answer 18

photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light

Question 19

What is chlorophyll and its function

Answer 19

Chlorophyll is a green pigment that is found in chloroplasts within plant cells
It is this pigment which gives plants their characteristic green colour
Chlorophyll transfers energy from light into energy in chemicals, for the synthesis of carbohydrates
It is essential for photosynthesis to occur

Question 20

How are the products of photosynthesis used

Answer 20

Converted into starch molecules which act as an effective energy store
Converted into cellulose to build cell walls
Glucose can be used in respiration to provide energy
Converted to sucrose for transport in the phloem
As nectar to attract insects for pollination
Plants can also convert the carbohydrates made into lipids for an energy source in seeds and into amino acids (used to make proteins) when combined with nitrogen and other mineral ions absorbed by roots

Question 21

Explain briefly how each of these features of a leaf are adaptations for photosynthesis
1 large surface area
2 Being thin

Answer 21

The large surface area allows large amounts of sunlight to fall on the leaf. The large surface area also increases the rate at which carbondioxide diffuse into the leaf from the air

Being thin means that sunlight can pass through the leaf, allowing many cells inside it to photosynthesis
The thinnes also helps carbondioxide to reach all the cells quite quickly by diffusion

Question 22

Describe the functions of upper epidermis cell

Answer 22

The cells in this layer are packed tightly together, to reduce the quantity of water vapour escaping from the leaf. They do not contain chloroplast so they cannot photosynthesis
This cells secrete (make and realease) a waxy substance which forms a thin, transparent, waterproof of covering called the cuticle

Question 23

Describe the function and strucuture of Palisade mesophyll cell

Answer 23

This is made of tall narrow cells containing a very large number of chloroplasts. Their main function is photosynthesis. As they are close to the top of leaf, they get plenty of sunlight. The transparent epidermis cells above them let the sunlight through easily.

Question 24

Describe the structure and the function of spongy mesophyll cell

Answer 24

The cells in the tissue also contain chloroplasts, but not as many as palisade cells. They are not as tightly packed either. There are many air spaces between them. These spaces allows carbon dioxide and oxygen to diffuse between the air and the cells inside the leaf.

Question 25

Describe the structure of stomata

Answer 25

Each stoma is surrounded by a pair of guard cells. The guard cells, unlike the other cells in the epidermis contain chloroplasts. The guard cells can change their shape which can open and close the stomata. The stomata allow diffusion of carbon dioxide and oxygen in and out of the leaf. Water vapour also diffuses out of the leaf through the stomata

Question 26

What are the two main role of bile

Answer 26

It is alkaline to neutralise the hydrochloric acid which comes from the stomach
The enz ymes in the small intestine have a higher(more alkaline) optimum pH than those in the
stomach
It breaks down large drops of fat into smaller ones. This is known as emulsification. The larger
surface area allows lipase to chemicallybreak down the lipid into glycerol and fattyacids faster

Question 27

Where is amylase produced

Answer 27

Amylases are produced in the mouth and the pancreas (secreted into the duodenum)
Amylases digest starch into smaller sugars

Question 28

Which acid is produced in the stomach

Answer 28

The stomach produces several fluids which together are known as gastric juice
One ofthe fluids produced is hydrochloric acid
This kills bacteria in food and gives an acid pH for enzymes to work in the stomach

Question 28

What are Proteases

Answer 28

Proteases are a group of enzymes that break down proteins into amino acids in the stomach
and small intestine (with the enz ymes in the small intestine having been produced in the pancreas)

Question 28

What are lipases

Answer 28

Lipase enzymes are produced in the pancreas and secreted into the duodenum
They digest lipids into fatty acids and glycerol

Question 29

How is a low pH helpful in the stomach?

Answer 29

The low pH kills bacteria in food that we have ingested as it denatures the enzymes in their cells,
meaning theycannot carryout anycell reactions to maintain life
Pepsin,produced in the stomach, is an example of an enz yme which has a verylow optimum pH -
around pH 2
The hydrochloric acid produced in the stomach ensures that conditions in the stomach remain
within the optimum range forpepsin to work at its fastest rate

Question 29

Where is amylase secreted

Answer 29

Amylase is secreted into the alimentarycanal in the mouth and the duodenum (from the
pancreas) and digests starch to maltose (a disaccharide)
Maltose is digested bythe enz yme maltase into glucose on the membranes ofthe epithelium
lining ofthe small intestine

Question 30

Where does protein digestion takes place

Answer 30

Protein digestion takes place in the stomach and duodenum with two main enz ymes produced:
Pepsin is produced in the stomach and breaks downprotein in acidic conditions
Trypsin is produced in the pancreas and secreted into the duodenum where is breaks down
protein in alkaline conditions

Question 31

What is absorption

Answer 31

Absorption is the movement of digested food molecules from the digestive system into the
blood (glucose and amino acids) and lymph (fattyacids and glycerol)
Nutrients are absorbed in the small intestine

Question 32

What are the adaptations of small intestine

Answer 32

The ileum is adapted for absorption as it is very long and has a highly folded surface with
millions of villi (tiny, fingerlike projections)
These adaptations massively increase the surface area ofthe ileum, allowing absorption to take
place faster and more efficientl

Question 33

State the function of microvilli

Answer 33

Microvilli on the surface ofthe villus furtherincrease surface area forfaster absorption of
nutrients
Wall ofthe villus is one cell thick meaning that there is onlya short distance for absorption to
happen bydiffusion and active transport
Well supplied with a network of blood capillaries that transport glucose and amino acids away
from the small intestine in the blood
Lactealruns through the centre ofthe villus to transportfattyacids and glycerol awayfrom the
small intestine in the lymph

Question 34

Describe xylem and its adaptations

Answer 34

Xylem vessels – transport water and minerals (pronounced: zi-lem) from the roots to the stem and leaves
Adaptations:
Cells joined end to end with no cross walls to form a long continuous tube
Cells are essentially dead, without cell contents, to allow free passage of water
Outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant

Question 35

Describe the structure of root haircells

Answer 35

Root hairs are single-celled extensions of epidermis cells in the root
They grow between soil particles and absorb water and minerals from the soil
Water enters the root hair cells by osmosis
This happens because soil water has a higher water potential than the cytoplasm of the root hair cell

The root hair increases the surface area of the cells significantly
This large surface area is important as it increases the rate of the absorption of water by osmosis and mineral ions by active transport

Question 36

Define Transpiration

Answer 36

Transpiration is defined as the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata

Question 37

What are the functions of transpiration in plants

Answer 37

Transpiration has several functions in plants:
transporting mineral ions
providing water to keep cells turgid in order to support the structure of the plant
providing water to leaf cells for photosynthesis
keeping the leaves cool (the conversion of water (liquid) into water vapour (gas) as it leaves the cells and enters the airspace requires heat energy. The using up of heat to convert water into water vapour helps to cool the plant down)

Question 38

What are the soluble products of photosynthesis and where is it transported

Answer 38

The soluble products of photosynthesis are sugars (mainly sucrose) and amino acids
These are transported around the plant in the phloem tubes which are made of living cells (as opposed to xylem vessels which are made of dead cells)
The cells are joined end to end and contain holes in the end cell walls (called sieve plates) which allow easy flow of substances from one cell to the next

Question 39

Define Translocation

Answer 39

The transport of sucrose and amino acids in the phloem, from regions of production to regions of storage or use, is called translocation

Question 40

Define source and sink

Answer 40

Transport in the phloem goes in many different directions depending on the stage of development of the plant or the time of year; however dissolved food is always transported from the source (where it’s made) to sink (where it’s stored or used):