OCR A2 Biology Lesson 6 | A-Level Revision Course

img.wp-smiley,img.emoji{display:inline !important;border:none !important;box-shadow:none !important;height:1em !important;width:1em !important;margin:0 .07em !important;vertical-align:-.1em !important;background:none !important;padding:0 !important;}.has-text-align-justify{text-align:justify;}.safe-svg-cover{text-align:center;}.safe-svg-cover .safe-svg-inside{display:inline-block;max-width:100%;}.safe-svg-cover svg{height:100%;max-height:100%;max-width:100%;width:100%;}.wp-block-restrict-content-pro-content-upgrade-redirect .wp-block-button__width-25{width:calc(25% - .5rem);}.wp-block-restrict-content-pro-content-upgrade-redirect .wp-block-button__width-25 .wp-block-button__link{width:100%;}.wp-block-restrict-content-pro-content-upgrade-redirect .wp-block-button__width-50{width:calc(50% - .5rem);}.wp-block-restrict-content-pro-content-upgrade-redirect .wp-block-button__width-50 .wp-block-button__link{width:100%;}.wp-block-restrict-content-pro-content-upgrade-redirect .wp-block-button__width-75{width:calc(75% - .5rem);}.wp-block-restrict-content-pro-content-upgrade-redirect .wp-block-button__width-75 .wp-block-button__link{width:100%;}.wp-block-restrict-content-pro-content-upgrade-redirect .wp-block-button__width-100{margin-right:0;width:100%;}.wp-block-restrict-content-pro-content-upgrade-redirect .wp-block-button__width-100 .wp-block-button__link{width:100%;}.jetpack-sharing-buttons__services-list{display:flex;flex-direction:row;flex-wrap:wrap;gap:0;list-style-type:none;margin:5px;padding:0;}.jetpack-sharing-buttons__services-list.has-small-icon-size{font-size:12px;}.jetpack-sharing-buttons__services-list.has-normal-icon-size{font-size:16px;}.jetpack-sharing-buttons__services-list.has-large-icon-size{font-size:24px;}.jetpack-sharing-buttons__services-list.has-huge-icon-size{font-size:36px;}@media print{.jetpack-sharing-buttons__services-list{display:none !important;}}.editor-styles-wrapper .wp-block-jetpack-sharing-buttons{gap:0;padding-inline-start:0;}ul.jetpack-sharing-buttons__services-list.has-background{padding:1.25em 2.375em;}.wp-block-rank-math-toc-block nav ol{counter-reset:item;}.wp-block-rank-math-toc-block nav ol li{display:block;}.wp-block-rank-math-toc-block nav ol li:before{content:counters(item,".") ". ";counter-increment:item;}.wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em;}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none;}body .is-layout-flow > .alignleft{float:left;margin-inline-start:0;margin-inline-end:2em;}body .is-layout-flow > .alignright{float:right;margin-inline-start:2em;margin-inline-end:0;}body .is-layout-flow > .aligncenter{margin-left:auto !important;margin-right:auto !important;}body .is-layout-constrained > .alignleft{float:left;margin-inline-start:0;margin-inline-end:2em;}body .is-layout-constrained > .alignright{float:right;margin-inline-start:2em;margin-inline-end:0;}body .is-layout-constrained > .aligncenter{margin-left:auto !important;margin-right:auto !important;}body .is-layout-constrained > :where(:not(.alignleft):not(.alignright):not(.alignfull)){max-width:var(--wp--style--global--content-size);margin-left:auto !important;margin-right:auto !important;}body .is-layout-constrained > .alignwide{max-width:var(--wp--style--global--wide-size);}body .is-layout-flex{display:flex;}body .is-layout-flex{flex-wrap:wrap;align-items:center;}body .is-layout-flex > *{margin:0;}body .is-layout-grid{display:grid;}body .is-layout-grid > *{margin:0;}.has-black-color{color:var(--wp--preset--color--black) !important;}.has-cyan-bluish-gray-color{color:var(--wp--preset--color--cyan-bluish-gray) !important;}.has-white-color{color:var(--wp--preset--color--white) !important;}.has-pale-pink-color{color:var(--wp--preset--color--pale-pink) !important;}.has-vivid-red-color{color:var(--wp--preset--color--vivid-red) !important;}.has-luminous-vivid-orange-color{color:var(--wp--preset--color--luminous-vivid-orange) !important;}.has-luminous-vivid-amber-color{color:var(--wp--preset--color--luminous-vivid-amber) !important;}.has-light-green-cyan-color{color:var(--wp--preset--color--light-green-cyan) !important;}.has-vivid-green-cyan-color{color:var(--wp--preset--color--vivid-green-cyan) !important;}.has-pale-cyan-blue-color{color:var(--wp--preset--color--pale-cyan-blue) !important;}.has-vivid-cyan-blue-color{color:var(--wp--preset--color--vivid-cyan-blue) !important;}.has-vivid-purple-color{color:var(--wp--preset--color--vivid-purple) !important;}.has-black-background-color{background-color:var(--wp--preset--color--black) !important;}.has-cyan-bluish-gray-background-color{background-color:var(--wp--preset--color--cyan-bluish-gray) !important;}.has-white-background-color{background-color:var(--wp--preset--color--white) !important;}.has-pale-pink-background-color{background-color:var(--wp--preset--color--pale-pink) !important;}.has-vivid-red-background-color{background-color:var(--wp--preset--color--vivid-red) !important;}.has-luminous-vivid-orange-background-color{background-color:var(--wp--preset--color--luminous-vivid-orange) !important;}.has-luminous-vivid-amber-background-color{background-color:var(--wp--preset--color--luminous-vivid-amber) !important;}.has-light-green-cyan-background-color{background-color:var(--wp--preset--color--light-green-cyan) !important;}.has-vivid-green-cyan-background-color{background-color:var(--wp--preset--color--vivid-green-cyan) !important;}.has-pale-cyan-blue-background-color{background-color:var(--wp--preset--color--pale-cyan-blue) !important;}.has-vivid-cyan-blue-background-color{background-color:var(--wp--preset--color--vivid-cyan-blue) !important;}.has-vivid-purple-background-color{background-color:var(--wp--preset--color--vivid-purple) !important;}.has-black-border-color{border-color:var(--wp--preset--color--black) !important;}.has-cyan-bluish-gray-border-color{border-color:var(--wp--preset--color--cyan-bluish-gray) !important;}.has-white-border-color{border-color:var(--wp--preset--color--white) !important;}.has-pale-pink-border-color{border-color:var(--wp--preset--color--pale-pink) !important;}.has-vivid-red-border-color{border-color:var(--wp--preset--color--vivid-red) !important;}.has-luminous-vivid-orange-border-color{border-color:var(--wp--preset--color--luminous-vivid-orange) !important;}.has-luminous-vivid-amber-border-color{border-color:var(--wp--preset--color--luminous-vivid-amber) !important;}.has-light-green-cyan-border-color{border-color:var(--wp--preset--color--light-green-cyan) !important;}.has-vivid-green-cyan-border-color{border-color:var(--wp--preset--color--vivid-green-cyan) !important;}.has-pale-cyan-blue-border-color{border-color:var(--wp--preset--color--pale-cyan-blue) !important;}.has-vivid-cyan-blue-border-color{border-color:var(--wp--preset--color--vivid-cyan-blue) !important;}.has-vivid-purple-border-color{border-color:var(--wp--preset--color--vivid-purple) !important;}.has-vivid-cyan-blue-to-vivid-purple-gradient-background{background:var(--wp--preset--gradient--vivid-cyan-blue-to-vivid-purple) !important;}.has-light-green-cyan-to-vivid-green-cyan-gradient-background{background:var(--wp--preset--gradient--light-green-cyan-to-vivid-green-cyan) !important;}.has-luminous-vivid-amber-to-luminous-vivid-orange-gradient-background{background:var(--wp--preset--gradient--luminous-vivid-amber-to-luminous-vivid-orange) !important;}.has-luminous-vivid-orange-to-vivid-red-gradient-background{background:var(--wp--preset--gradient--luminous-vivid-orange-to-vivid-red) !important;}.has-very-light-gray-to-cyan-bluish-gray-gradient-background{background:var(--wp--preset--gradient--very-light-gray-to-cyan-bluish-gray) !important;}.has-cool-to-warm-spectrum-gradient-background{background:var(--wp--preset--gradient--cool-to-warm-spectrum) !important;}.has-blush-light-purple-gradient-background{background:var(--wp--preset--gradient--blush-light-purple) !important;}.has-blush-bordeaux-gradient-background{background:var(--wp--preset--gradient--blush-bordeaux) !important;}.has-luminous-dusk-gradient-background{background:var(--wp--preset--gradient--luminous-dusk) !important;}.has-pale-ocean-gradient-background{background:var(--wp--preset--gradient--pale-ocean) !important;}.has-electric-grass-gradient-background{background:var(--wp--preset--gradient--electric-grass) !important;}.has-midnight-gradient-background{background:var(--wp--preset--gradient--midnight) !important;}.has-small-font-size{font-size:var(--wp--preset--font-size--small) !important;}.has-medium-font-size{font-size:var(--wp--preset--font-size--medium) !important;}.has-large-font-size{font-size:var(--wp--preset--font-size--large) !important;}.has-x-large-font-size{font-size:var(--wp--preset--font-size--x-large) !important;}.wp-block-navigation a:where(:not(.wp-element-button)){color:inherit;}.wp-block-pullquote{font-size:1.5em;line-height:1.6;}#site-navigation,.navigation-clone,#mobile-header{display:none !important;}a:hover,a:focus,a:active{color:#000;}.wp-block-group__inner-container{max-width:1100px;margin-left:auto;margin-right:auto;}input,select,textarea{font-family:"Nunito",sans-serif;font-size:18px;}.entry-content > [class*="wp-block-"]:not(:last-child){margin-bottom:1.5em;}.main-navigation .main-nav ul ul li a{font-size:14px;}.sidebar .widget,.footer-widgets .widget{font-size:17px;}h3{font-size:20px;}h4{font-size:inherit;}h5{font-size:inherit;}.top-bar{background-color:#636363;color:#fff;}.top-bar a{color:#fff;}.top-bar a:hover{color:#303030;}.main-title a:hover{color:#fff;}.site-description{color:#757575;}.main-navigation .main-nav ul li a,.menu-toggle,.main-navigation .menu-bar-items{color:#fff;}.main-navigation .main-nav ul li:hover > a,.main-navigation .main-nav ul li:focus > a,.main-navigation .main-nav ul li.sfHover > a,.main-navigation .menu-bar-item:hover > a,.main-navigation .menu-bar-item.sfHover > a{color:#fff;background-color:#3d444b;}button.menu-toggle:hover,button.menu-toggle:focus,.main-navigation .mobile-bar-items a,.main-navigation .mobile-bar-items a:hover,.main-navigation .mobile-bar-items a:focus{color:#fff;}.main-navigation .main-nav ul li[class*="current-menu-"] > a{color:#fff;}.main-navigation .main-nav ul li[class*="current-menu-"] > a:hover,.main-navigation .main-nav ul li[class*="current-menu-"].sfHover > a{color:#fff;}.navigation-search input[type="search"],.navigation-search input[type="search"]:active,.navigation-search input[type="search"]:focus,.main-navigation .main-nav ul li.search-item.active > a,.main-navigation .menu-bar-items .search-item.active > a{color:#fff;background-color:#3d444b;}.main-navigation ul ul{background-color:#3d444b;}.main-navigation .main-nav ul ul li a{color:#fff;}.main-navigation .main-nav ul ul li:hover > a,.main-navigation .main-nav ul ul li:focus > a,.main-navigation .main-nav ul ul li.sfHover > a{color:#fff;background-color:#2c3338;}.main-navigation .main-nav ul ul li[class*="current-menu-"] > a{color:#fff;background-color:#3d444b;}.main-navigation .main-nav ul ul li[class*="current-menu-"] > a:hover,.main-navigation .main-nav ul ul li[class*="current-menu-"].sfHover > a{color:#fff;background-color:#3d444b;}.separate-containers .comments-area,.separate-containers .page-header,.one-container .container,.separate-containers .paging-navigation,.inside-page-header{background-color:#fff;}.entry-meta{color:#595959;}.entry-meta a{color:#595959;}.entry-meta a:hover{color:#1e73be;}.sidebar .widget{background-color:#fff;}.sidebar .widget .widget-title{color:#000;}.footer-widgets{background-color:#fff;}.footer-widgets .widget-title{color:#d63638;}.site-info{color:#fff;background-color:#3d444b;}.site-info a{color:#fff;}.site-info a:hover{color:#606060;}.footer-bar .widget_nav_menu .current-menu-item a{color:#606060;}input[type="text"],input[type="email"],input[type="url"],input[type="password"],input[type="search"],input[type="tel"],input[type="number"],textarea,select{color:#666;background-color:#fafafa;border-color:#ccc;}input[type="text"]:focus,input[type="email"]:focus,input[type="url"]:focus,input[type="password"]:focus,input[type="search"]:focus,input[type="tel"]:focus,input[type="number"]:focus,textarea:focus,select:focus{color:#666;background-color:#fff;border-color:#bfbfbf;}html input[type="button"],input[type="reset"],input[type="submit"],a.button,a.wp-block-button__link:not(.has-background){color:#ebf7f1;background-color:#00a32a;}button:hover,html input[type="button"]:hover,input[type="reset"]:hover,input[type="submit"]:hover,a.button:hover,button:focus,html input[type="button"]:focus,input[type="reset"]:focus,input[type="submit"]:focus,a.button:focus,a.wp-block-button__link:not(.has-background):active,a.wp-block-button__link:not(.has-background):focus,a.wp-block-button__link:not(.has-background):hover{color:#fff;background-color:#008a20;}a.generate-back-to-top{background-color:rgba(0,0,0,.4);color:#fff;}a.generate-back-to-top:hover,a.generate-back-to-top:focus{background-color:rgba(0,0,0,.6);color:#fff;}.inside-top-bar{padding:10px;}.entry-content .alignwide,body:not(.no-sidebar) .entry-content .alignfull{margin-left:-40px;width:calc(100% + 80px);max-width:calc(100% + 80px);}.rtl .menu-item-has-children .dropdown-menu-toggle{padding-left:20px;}.rtl .main-navigation .main-nav ul li.menu-item-has-children > a{padding-right:20px;}.site-info{padding:20px;}.one-container .sidebar .widget{padding:0px;}.dynamic-author-image-rounded{border-radius:100%;}.dynamic-featured-image,.dynamic-author-image{vertical-align:middle;}.one-container.blog .dynamic-content-template:not(:last-child),.one-container.archive .dynamic-content-template:not(:last-child){padding-bottom:0px;}.dynamic-entry-excerpt > p:last-child{margin-bottom:0px;}body.modal-open #wpadminbar{z-index:999;}.embed-responsive-16by9 .fluid-width-video-wrapper{padding:0 !important;position:initial;}.getpaid-price-buttons label{transition:all .3s ease-out;text-align:center;padding:10px 20px;background-color:#eee;border:1px solid #e0e0e0;}.getpaid-price-circles label{padding:0 4px;-moz-border-radius:50%;-webkit-border-radius:50%;border-radius:50%;}.getpaid-price-circles label span{display:block;padding:50%;margin:-3em -50% 0;position:relative;top:1.5em;border:1em solid transparent;white-space:nowrap;}.getpaid-price-buttons input[type="radio"]{visibility:hidden;height:0;width:0 !important;}.getpaid-price-buttons input[type="radio"]:checked + label,.getpaid-price-buttons label:hover{color:#fff;background-color:#1e73be;border-color:#1e73be;}.getpaid-public-items-archive-single-item .inner{box-shadow:0 1px 3px rgba(0,0,0,.12),0 1px 2px rgba(0,0,0,.24);}.getpaid-public-items-archive-single-item:hover .inner{box-shadow:0 1px 4px rgba(0,0,0,.15),0 1px 3px rgba(0,0,0,.3);}.wp-block-getpaid-public-items-getpaid-public-items-loop .item-name{font-size:1.3rem;}.getpaid-subscription-item-actions{color:#ddd;font-size:13px;padding:2px 0 0;position:relative;left:-9999em;}.getpaid-subscriptions-table-row:hover .getpaid-subscription-item-actions{position:static;}.getpaid-subscriptions table{font-size:.9em;table-layout:fixed;}.getpaid-subscriptions-table-column-subscription{font-weight:500;}.getpaid-subscriptions-table-row span.label{font-weight:500;}.getpaid-subscriptions.bsui .table-bordered thead th{border-bottom-width:1px;}.getpaid-subscriptions.bsui .table-striped tbody tr:nth-of-type(odd){background-color:rgba(0,0,0,.01);}.wpinv-page .bsui a.btn{text-decoration:none;margin-right:2px;margin-bottom:2px;}.getpaid-cc-card-inner{max-width:460px;}.getpaid-form-cart-item-price{min-width:120px !important;}#primary .getpaid-payment-form p{float:none !important;}.bsui .is-invalid ~ .invalid-feedback,.bsui .is-invalid ~ .invalid-tooltip{display:block;}.bsui .is-invalid{border-color:#dc3545 !important;}.getpaid-file-upload-element{height:200px;border:3px dashed #dee2e6;cursor:pointer;}.getpaid-file-upload-element:hover{border:3px dashed #424242;}.getpaid-file-upload-element.getpaid-trying-to-drop{border:3px dashed #8bc34a;background:#f1f8e9;}img#wpstats{display:none;}