OCR A Level Biology: Cells, Exchange
and Transport
Before the division of the nucleus of a cell, the genetic material must replicate
Explain why this is essential - ANS-Daughter cells have genetically identical DNA so both cells
receive a full copy
\Describe how active loading takes place - ANS-Hydrogen ions pumped out of the companion
cell, increasing hydrogen ion concentration outside of the companion cell.
Hydrogen ions re-enter the companion cells, and sugar moves with the hydrogen ions
Down concentration gradient by facilitated diffusion
Sucrose diffuses into sieve tubes, through plasmodesmata
\Describe the pressure changes in the blood as it flows through the circulatory system from the
aorta to the veins - ANS-Pressure drops as distance from heart increases
Greatest pressure drop while blood is in the arteries
Pressure does not drop in veins
Fluctuation decreases from aorta to arteries
No fluctuation in capillaries
\Explain what is meant by a homologous pair of chromosomes - ANS-One maternal and one
paternal chromosome
Carry the same genes
Centromere in same position
Same banding pattern
Pair up in mitosis/form bivalent
\Explain why it is important that the pressure changes as blood flows from the aorta to the
capillaries - ANS-Capillary walls are thin/one cell thick
High pressure would burst/damage capillary wall
Reduce chance of tissue build up
\Explain why red blood cells burst when in contact with distilled water, but plant cells do not -
ANS-Cell cytoplasm has lower water potential than pure/distilled water
Water moves into cells down the water potential gradient and enters cells by osmosis
Plasma membrane is weak and therefore bursts as it cannot withstand the pressure
Plant cell wall is strong and provides support so it does not burst/can withstand high pressure
Plant cell becomes turgid which reduces water uptake
\Function of ciliated epithelium - ANS-Move mucus
\Function of squamous epithelium - ANS-Acts as a surface
Short diffusion distance
\Identify two features visible in a eukaryotes that would not be present in a prokaryotic cells -
ANS-Nucleus/nuclear envelope
Mitochondria
Rough endoplasmic reticulum
Golgi apparatus
and Transport
Before the division of the nucleus of a cell, the genetic material must replicate
Explain why this is essential - ANS-Daughter cells have genetically identical DNA so both cells
receive a full copy
\Describe how active loading takes place - ANS-Hydrogen ions pumped out of the companion
cell, increasing hydrogen ion concentration outside of the companion cell.
Hydrogen ions re-enter the companion cells, and sugar moves with the hydrogen ions
Down concentration gradient by facilitated diffusion
Sucrose diffuses into sieve tubes, through plasmodesmata
\Describe the pressure changes in the blood as it flows through the circulatory system from the
aorta to the veins - ANS-Pressure drops as distance from heart increases
Greatest pressure drop while blood is in the arteries
Pressure does not drop in veins
Fluctuation decreases from aorta to arteries
No fluctuation in capillaries
\Explain what is meant by a homologous pair of chromosomes - ANS-One maternal and one
paternal chromosome
Carry the same genes
Centromere in same position
Same banding pattern
Pair up in mitosis/form bivalent
\Explain why it is important that the pressure changes as blood flows from the aorta to the
capillaries - ANS-Capillary walls are thin/one cell thick
High pressure would burst/damage capillary wall
Reduce chance of tissue build up
\Explain why red blood cells burst when in contact with distilled water, but plant cells do not -
ANS-Cell cytoplasm has lower water potential than pure/distilled water
Water moves into cells down the water potential gradient and enters cells by osmosis
Plasma membrane is weak and therefore bursts as it cannot withstand the pressure
Plant cell wall is strong and provides support so it does not burst/can withstand high pressure
Plant cell becomes turgid which reduces water uptake
\Function of ciliated epithelium - ANS-Move mucus
\Function of squamous epithelium - ANS-Acts as a surface
Short diffusion distance
\Identify two features visible in a eukaryotes that would not be present in a prokaryotic cells -
ANS-Nucleus/nuclear envelope
Mitochondria
Rough endoplasmic reticulum
Golgi apparatus
