3.3 Organisms exchange substances with their environment Flashcards
1
Q
3.3.1 Surface Area to Volume Ratio
How does an organisms size relate to their surface area to volume ratio?
A
- The larger the organism, the smaller its surface area to volume ratio
2
Q
How does an organisms surface area to volume ratio relate to their metabolic rate?
A
- The smaller the surface area to volume ratio, the higher the metabolic rate
3
Q
How might a large organism adapt to compensate for its small surface area to volume ratio?
A
- changes that will increase that surface area for example body parts becoming larger, developing a specialised gas exchange surface
4
Q
Why do multicellular organisms require specialised gas exchange surfaces?
A
- Due to having a smaller SA:V ratio, the distanced that needs to be crossed for the gases is larger
- substances cannot easily enter the cells as in single celled organism
5
Q
3.3.2 Gas Exchange
What are three key features that make an efficient gas exchange surface?
A
- Large surface area
- Thin/short diffusion pathway
- Steep concentration gradient
6
Q
Why cant insects use their bodys as an exchange surface?
A
- They have a waterproof exoskeleton made from chitin
- and a small SA:V in order to conserve water
7
Q
-
What are the three main features of an insects gas exchange system?
A
- Spiracles- holes on the bodys surface which open and close by a valve for gas or water exchange
- Tracheae- large tubes extending through all body tissues, supported by rings so they dont collapse
- Tracheoles-small branches coming off the tracheae
8
Q
What are 3 ways the insect tracheal system is adapted for efficient gas exchange?
A
- Lots of tracheoloes-so larger surface area for gas exchange
- Fine/thin tracehole walls-shorter diffusion distance to cells
- Spiracles on the bodys surface which open and close by a valve for gas
9
Q
Explain the process of gas exchange in insects
A
- Gases move in and out of the tracheae through the spiracles
- A diffusion gradient allows oxygen to diffuse into the body tissue and waste CO2 diffuses out
- Contraction of muscles in the trachea allows the mass movement of air in and out
10
Q
Why cant fish use their bodys as an exchange surface?
A
- They have a waterproof, impermeable outer membrane and a small SA:V ratio
- instead they use a specialised gas exchange system
11
Q
What are the two main features of a fishs gas exchange system?
A
- Gills- located within the body, have lots of gill filaments which are stacked up in piles
- Lamellae- at right angles to the gill filaaments which give and increased surface area. BLood and water flow across them in opposite directions (countercurrent mechanism)
12
Q
What are 3 ways the fish is adapted for efficient gas exhange?
A
- lots of gill filaments-larger SA:V ratio for gases
- thinner lamellae- shorter diffusion distance
- countercurrent mechanism
13
Q
Explain the process of gas exchange in fish?
A
- the fish opens its mouth to enable water to flow in, then closes its mouth to increase presuure
- the water passes over the lamallae, and the oxygen diffuses into the bloodstream
- waste carbon dioxide diffuses into the water and flows back out the gills
14
Q
Explain the countercurrent mechanism
A
- Water and blood flow over the gills in opposite directions
- This maintains a steep concentration gradient over the along the length of the whole lamellae
- ensures equilibrium is not reached
15
Q
Name and describe three adaptations of a leaf that allows efficient gas exchange
A
- thin and flat-short diffusion pathway, large SA:V ratio
- many stomata-allows gases to easily enter
- air spaces in the mesophyll allows gases to move around the leaf, facilitating photosynthesis
16
Q
How do plants limit their water loss while still allowing gases to be exchanged?
A
- Stomata regulated by guard cells which allows them to open and close as needed
- most stay closed to prevent water loss while some open to let oxygen in
17
Q
Describe the pathway taken by air as it enters the mammalian gaseous exchange system
A
- Nasal cavity–> trachea–> bronchi–>bronchioles–>alveoli
18
Q
What is the function of the nasal cavity in the mammalian gaseous exchnage system?
A
- a good blood supply warms and moistens the air entering the lungs
- Goblet cells in membrane secrete mucus which trap dust and bacteria
19
Q
Describe the trachea and its function in the mammalian gas exchange system
A
- wide tube supported by C-shaped cartilige to keep the air passage open during pressure changes
- lined by ciliated epithelium cells which move mucus towards the throat to be swallowed preventing lung infections
- carries air to the bronchi
20
Q
Describe the bronchi and their function in the mammalian gaseous exchange system
A
- Like the trachea they are supported by rings of cartilage and are lined by ciliated epithelium cells
- however they are narrower and there are two of them, one for each lung
- allows passage of air into bronchioles
21
Q
Describe the bronchioles and their function in the mammalian gaseous exchange system
A
- narrower than the bronchi
- do not need to be kept open by cartilage therefore mostly have only muscle and elastic fibres so that they can contract and relax easily during ventilation
- allos passage of air into alveoli
22
Q
Describe the alveoli and their function in the mammalian gas exchange system
A
- mini air sacs lined with epithelium cells, site of gas exchange
- walls only one cell thick, covered with a network of capillaries which facilitates gas diffusion
23
Q
Explain the process of inhalation/inspiration
A
- External intercostal muscles contract (while internal relax) pulling the ribs UP and OUT
- Diaphragm contracts and flattens
- Volume of thorax increases
- Air pressure outside the lungs is therefore higher than the air pressure inside so air moves in to rebalance
24
Q
Explain the process of exhalation/expiration
A
- External intercostal muscles relax while internal intercostal muscles contract bringing the ribs DOWN and IN
- Diaphragm relaxes and it domes upwards
- volume in thorax decreases
- Air pressure inside the lungs is therefore higher than the air pressure outside, so air moves out to rebalance
25
What is tidal volume?
* the volume of air we breathe in and out during each breath at rest
26
What is breathing rate?
* the number of breaths we take per minute
27
How do you calculate pulmonary ventilation rate?
* tidal volume x breathing rate
* can be measured using a spirometer which is a device that records volume changes onto a graph as a person breathes
28
# ***3.3.3 Digestion and Absorption***
What is digestion?
* the hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes
29
Which enzymes are involved in carbohydrate digestions and where are they found?
* Amylase-mouth
* Maltase, sucrase, lactase-membrane of small intestine
30
What are the substrates and products of the carbohydrate digestive enzymes?
* Amylase--> starch into smaller polysaccharides
* Maltase--> maltose into 2x glucose
* Sucrase--> sucrose into glucose and fructose
* Lactase--> lactose into glucose and galactose
31
Where are lipids digested?
* the small intestine
32
What needs to happen before lipids can be digested?
* They **must be emulsified by bile salts produced in the liver**
* this **breaks down large fat molecules** into **smaller, soluble molecules called micelles**, **increasing surface area**
33
What is the role of micelles in the absorption of lipids?
* are water soluble
* increase surface area for absorption
34
How are lipids digested?
* lipase hydrolyse the ester bond between monoglycerides and fatty acids
35
How is the ileum adapted for efficient absorption?
* wall is covered in **villi** which have **thin walls** surrounded by a network of capillaries and epithelial cells have even smaller **microvilli**
* these features maximisie absorption by **increasing the surface area**, **decreasing the diffusion distance** and **maintaining a concentration gradient
36
Which enzymes are involved in protein digestion and what are their roles?
* **Endopeptidases**-break between specific amino acids in the **MIDDLE** of a polypeptide
* **Exopeptidases**- break specific amino acids at the **END** of a polypeptide
* **Dipeptidases**-break **dipeptides into amino acids**
37
How are certain molecules absorbed into the ileum despite a negative concentration gradient?
* through co-transport
38
Which molecules require co-transport?
* amino acids
* monosaccharides
39
Explain how sodium ions are involved in co-transport
* Sodium ions **(Na+)** are **actively transported out** of the **cell** and **into the lumen**
* This **creates a diffusion gradient**
* **Nutrients** are then **taken up into the cells** along **with Na+ ions**
40
Why do fatty acids and monoglycerides not require co-transport?
* The molecules are non-polar, meaning they can easily diffuse across the membrane of the epithelial cells
41
# ***3.3.4 Mass Transport***
What is haemoglobin?
* a protein with a quatenary structure
42
Describe the structure of haemoglobin
* globular, water soluble
* consists of four polypeptide chains each carrying a haem group (quatenary structure)
43
Describe the role of haemoglobin
* present in red blood cells
* **oxygen molecules bind** to the **haem groups** and are **carried around the body** to where they are needed in **respiring tissues**
44
What three factors affect oxygen-haemoglobin binding?
* Partial pressure/concentration of oxygen
* partial pressure/concentration of carbon dioxide
* saturation of haemoglobin with oxygen
45
How does partial pressure of oxygen affect oxygen-haemoglobin binding?
* As **partial pressure** of **oxygen increases** the **affinity of haemoglobin for oxygen** also **increases**
* so **oxygen binds tightly to haemoglobin**
* when **partial pressure is low**, **oxygen** is **released from haemoglobin
46
How does partial pressure of
carbon dioxide affect oxygen-haemoglobin binding?
* As **partial pressure** of **carbon dioxide increases** the **conditions become acidic** which **causing haemoglobin to change shape**
* The **affinity** of **haemoglobin for oxygen** therefore **decreases** so **oxygen is released from haemoglobin**
* This is known as the **Bohr Effect**
47
How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?
* It is **hard** for the **first oxygen molecule to bind**
* Once it does **it changes the shape** to make it **easier for 2nd and 3rd molecules to bind** known as **positive cooperativity**
* It is then **slightly harder** for the **4th oxygen molecule to bind** because there is a **low chance of finding a binding site**
48
Why does oxygen bind to haemoglobin in the lungs?
* **partial pressure** of **oxygen** is **high**
* **low concentration of carbon dioxide** in the **lungs**, so **affinity is high**
* **Positive cooperativity** (after the first oxygen molecule binds, binding of subsequent molecules is easier)
49
Explain why oxygen is released from haemoglobin in respiring tissues
* **partial pressure** of **oxygen** is **low**
* **high concentration** of **carbon dioxide in respiring tissues** so **affinity decreases**
50
What do oxyhaemoglobin dissociation curves show?
* **saturation of haemoglobin with oxygen** plotted against **partial pressure of oxygen**
* **curves further** to the **left show** that **haemoglobin has** a **higher affinity for oxygen**
51
How does carbon dioxide affect the position of an oxyhaemoglobin dissociation curve?
* **curve shifts** to the **right** because **haemoglobins affinity** for **oxygen** has **decreased**
52
Name 3 common features of a mammalian circulatory system
* suitable medium for transport, water-based to allow substances to dissolve
* means of moving the medium and maintaining pressure throughout the body, such as the heart
* means of controlling flow so it remains unidirectional, such as valves
53
What are the 4 chambers of the heart?
* right atrium
* right ventricle
* left atrium
* left ventricle
54
Relate the structure of the chambers to their function
* **Atria**-**thin walled** and **elastic**, so they **can stretch** when **filled with blood**
* **Ventricles**-**thick muscular walls**, **pump blood** under **high pressure**, **left ventricle** is **thicker** than the right **because** it has to **pump blood all the way around the body**
55
What are the main blood vessels in the heart?
* Arteries
* Veins
* Capillaries
56
Relate the structure of the vessels to their function
* **Arteries**- have **thick walls** to **handle pressure without tearing** and are **muscular** and **elastic to control blood flow**
* **Veins**- have **thin walls due** to **lower pressure** therefore **requiring valves** to **ensure blood doesnt flow backwards**. They have **less muscular and elastic tissue** as they **dont have to control blood flow**
57
Why are two pumps (left and right) needed instead of one?
* to **maintain blood pressure** around the **whole body**
* when **blood passes through** the **narrow capillaries** of the **lungs** the **pressure drops sharply** therefore **would NOT BE flowing strongly enough** to continue around the whole body
* therefore it is **returned to the heart to increase the pressure**
58
Describe what happens during cardiac diastole
* **The heart** is **relaxed**
* **Blood enters** the **atria** which **increases the pressure** and **pushing open the atrioventricular valves**
* This **allows blood** to **flow into the ventricles**
* **Pressure in heart** is **lower than** in the **arteries** so **semilunar valves remain closed**
59
Describe what happens during atrial systole
* The **atria contract**, **pushing remaining blood into** the **ventricles**
60
Describe what happens during ventricular systole
* The **ventricles contract**
* The **pressure increases** which **closes the atrioventricular valves** to **prevent backflow** and **semi-lunar valves open**
* **Blood flows into** the **arteries**
61
How is the structure of capillaries suited to their function?
* **walls** are only **one cell thick**-**short diffusion pathway**
* **very narrow** so can **permeate tissues** and **red blood cells can lie flat against the wall**, effectively **delivering oxygen to respiring cells**
* **numerous** and **highly branched** which creates **larger surface area**
62
What is tissue fluid?
* A watery substance
* Contains glucose, amino acids, oxygen and other nutrients
* It supplies these to the cells, while also **removing any waste materials**
63
How is tissue fluid formed and how is it returned to the circulatory system?
* **hydrostatic pressure of blood** is **high** at **arterial end**
* **water and fluids forced out**
* **large molecules remain** because **theyre to large**
* this **lowers the WP**
* **water moves back** into the **venous end of capillary via osmosis**
* **lymph system collects** any **excess tissue fluid** which **returns blood to the circulatotory system**
* **tissue fluid returned** to **vein
64
How is water transported in plants?
* **through xylem vessels**
* these are **long, continuos columns** that also **provide structural support to the stem**
65
Explain the cohesion-tension theory
* **water molecules form hydrogen bonds with each other**
* this causes them to **stick together (cohesion)**
* the **surface tension** of the **water** also **creates the sticking effect**
* therefore as **water is lost through transpiration**, **more can be drawn up the stem**
66
What are the three components of the phloem vessels?
* **sieve tube elements**- **form a tube** to **transport sucrose** in the **dissolved form of sap**
* **companion cells**- **involved** in **ATP production** for **active loading of sucrose** **into sieve tubes**
* **plasmodemesmata**- **gaps between cell walls** where the **cytoplasm links allowing substances to flow**
67
Name the process whereby organic materials are transported around the plant
* Translocation
68
How does sucrose in the leaf move into the phloem?
* **sucrose enters companion cells of the phloem vessels by active loading**
* this **uses ATP** and a **diffusion gradient of hydrogen ions**
* **sucrose then diffuses from companion cells** and **into sieve tube elements through** the **plasmodesmata**
69
How do phloem vessels transport sucrose around the plant?
* As **sucrose moves into the STE** the **WP inside** the **phloem** is **reduced**
* this causes **water to enter via osmosis from the xylem** and **increases hydrostatic pressure**
* **water moves along the STE** and **towards areas** of **lower hydrostatic pressure**
* **sucrose diffuses into surrounding cells** where it is needed
70
Give evidence for the mass flow hypothesis of translocation
* **Sap is released** when a **stem is cut** therefore there **must be pressure** in the **phloem**
* there is a **higher sucrose concentration** in the **leaves than in the roots**
* **increasing sucrose levels** in the **leaves** results in **increased sucroses in the phloem**
71
Give evidence against the mass flow hypothesis of translocation
* the **structure of STE** seems to **hinder mass flow**
* **not all solutes move** at the **same speed** as they would in mass flow
* **sucrose** is **delivered** at the **same rate** throughout the plant, rather than to areas with the lowest sucrose concentration first
72
How can ringing experiments be used to investigate transport in plants?
* the **bark** and **phloem** of a **tree** are **removed in a ring** which **leaves behind the xylem**
* the **tissues above the missing ring swells** **due to accumulation of sucrose** as the **tissue below begins to die**
* therefore **sucrose must be trsnsported in the phloem**
73
How can tracing experiments be used to investigate transport in plants?
* **plants are grown** in the **presence of radioactive CO2** which **will be incorporated into the plants sugars**
* using **autoradiography** we can **see the areas exposed to radiation correspond to where the phloem is**
